For much of the GEICO 400 race at Chicagoland Speedway on Sunday afternoon, Jimmie Johnson was completely in control. The five-time champion led 172 of the 267-lap, 400-mile race at the 1.5-mile oval - but ended up having to watch as Keselowski blended back onto the track in front of him after their final pit stops. The Penske Racing #2 then proceeded to pull away over the remaining laps of the race to claim the chequered flag and first blood in the 2012 Chase.

"It feels like round one of a heavyweight title bout," said Keselowski, who came away from Chicago with the points lead in the NASCAR Sprint Cup championship for the first time in his career as a result of the win. "It's a ten-round bout. Week one's done [but] we've got a lot of racing left to go."

Three hours earlier, as the cars came round to take the green flag for the first time, Dale Earnhardt Jr. was already finding himself going backwards fast. Having qualified in fourth place on the second row of the grid on Saturday afternoon, a mishap following the qualifying session forced the Hendrick team to change out the engine.

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"It slipped into third gear," said Earnhardt. "[I] over-revved it just for a split-second and a valve hit a piston in the third cylinder and we can't take any chances," he said, adding: "It didn't destroy anything, but we can't run [that engine] ... The valves and the piston had a little party and they all ended-up with a hangover!"

But even as his team mate Jimmie Johnson led the field away at the start with Earnhardt right at the other end of the line, he wasn't too downcast: "It's a good long race, the car is good enough," he insisted. "Fortunately, this is a racetrack that there are multiple pit strategies, and it's not a really simple straight-forward pit strategy to call. I think there will be a lot of opportunities."

So as the cars got up to speed, everyone settled down to see who was going to use what strategy to win the first race in the 2012 Chase. It was no surprise to see Johnson immediately shoot away at the front, or that his Hendrick team mate Kasey Kahne should also soon dispatch Aric Almirola and pull up into second place, by which time Johnson's lead was nearing the two second mark.

Earnhardt meanwhile was working his way back up through the field and finding some of it tough going, with a notable doorbanging incident with Trevor Bayne into turn 1 on lap 36 that fortunately resulted in no casualties, shortly before the first round of green flag pit stops which was relatively uneventful save for Travis Kvapil snagging his jack as he left his pit stall and dragged it round an entire lap before coming back in again to have the accessory removed.

Johnson and Kahne resumed at the front after the sequence concluded, with Denny Hamlin, Joey Logano and Matt Kenseth just about keeping in touch through to the first caution of the afternoon which was for debris in turn 2 on lap 66, which allowed the leaders to come in for a second time and have some adjustment as a side order to the serving of tyres and fuel. This time the notable double-stopper on pit road was Tony Stewart, who after his initial visit to his pit stall felt a decided vibration suggestion something was wrong with the new tyres, and he preferred to come back in for another changeover rather than risk losing one of the wheels off his wagon under green.

Johnson resumed in the lead although Kasey Kahne gave him an early run for hi money. With Jeff Gordon taking the restart in fifth and Earnhardt now joining his stablemates in the top ten at this point, it was looking like a very satisfactory day at the office for everyone wearing a Hendrick insignia.

Lap 100 was celebrated with the second debris caution of the day, and Brad Keselowski and Kevin Harvick stole a march on the others by taking only two tyres in the ensuing pit stops. That put them on the front row for the restart ahead of Johnson and Kahne: and nice the green came out, it was clear that Keselowski at least had the pace to stay right where he was on point He soon opened up a three car length led of just under a second over Johnson, who presumably was taking notes: make sure the #2 doesn't get in front when it comes down to the business end of the race, or it could cost him the win.

Unsurprisingly given the two-tyre strategy that had put him at the front, Keselowski's pace started to fall off as the next round of pit stops appeared and by lap 139 Johnson was close enough to have a look under the Penske car and start sizing up Keselowski for the overtake move. He hadn't managed to make the move stick when the third caution of the day came out, and for once it wasn't debris but an actual incident that was the cause - Casey Mears slapped the wall in turn 1 on lap 149.

"We just blew a right front, I don't know why," explained Mears. "We ran longer than even that right there on the first couple runs. We don't know why it happened but we had a pretty good car."

Johnson was able to beat Keselowski off pit road this time and settled back into the lead once more, with Kahne, Gordon and Ryan Newman taking up the rest of the top five at the green flag. Now it was Keselowski's turn to sit in second place and stare in frustration at another car's back end for a while, and jut as Johnson had found before him there was little he could do at this stage of the race without risking too much, too soon. Having two more Hendrick cars running immediately behind him would hardly have been settling for his nerves.

And then one of the Hendrick cars was gone: Jeff Gordon ploughed straight into the wall at turn 1 on lap 188 to bring out the fourth caution of the afternoon. A stuck throttle was to blame.

"We're still looking into it," said Gordon. "Something with the return spring where it didn't come all the way back. So, it was about half-throttle, which is better than full throttle, but it still caused a lot of damage and caused us to hit the wall and end our day.

"We were having a good day," he added. "Coming from 19th to be up there in the top five, and I don't know if we had anything to win the race, but we certainly were giving it everything we had and that's very disappointing."

It's a disaster for any hopes he had of figuring in the 2012 Chase after scraping in on the final "most wins" wildcard after last weekend's race at Richmond. Being listed with a 35th place finish in the results means that just one race into the ten-race shootout for the Sprint Cup championship he is already 47pts down from the leader - a full race's worth of points.

"In this deal, you can't afford to have issues like that," he ruefully agreed.

The race went back to green on lap 195 with Johnson, Keselowski and Kahne now joined at the front by Joe Gibbs Racing's non-Chase contenders Kyle Busch and Joey Logano for a time. A retirement for Dave Blaney whose car lost power on lap 204 was handled without recourse to yellows, and soon the final round of pit stops for the day were beginning.

Johnson and Kahne both came in on lap 229; Keselowski was able to eke out another lap and came in next time around. And when Keselowski exited pit lane, he pulled up right in front of the #48 - to the fury of Johnson and the Hendrick pit crew, who felt that Keselowski had clearly breached the rules regarding blending back in from the pit exit, and that the move had caused Johnson to check up to avoid a collision.

"He did cut up early. It did impede my progress, I had to check up and wasn't sure where things were going," insisted Johnson. "At the time it messed me up."

The NASCAR officials reviewed the video of the incident - and concluded that Keselowski had done nothing against the rules. No penalty would be forthcoming, so Johnson was left once again staring at the back of the Penske car and this time it had come at a critical moment: if the same situation repeated itself form earlier in the race, Johnson was going to have a real problem getting back around Keselowski for position.

Keselowski wasn't in the lead at this point, as it took until lap 242 before the final cars dived into pit lane and Keselowski was promoted to the top. That wasn't good news for Johnson, as that meant Keselowski also now had the best of the clear air up front, although slow lapped traffic minimised that edge somewhat and meant Keselowski had to stay sharp to avoid getting hung up anywhere.

But 'Special K' wasn't making any mistakes, and was calmly and methodically working the advantage he'd got from the pit exit manoeuvre to start pulling away from Johnson. As the final laps played it it was clear that the #48 had nothing in reserve and could only watch the leader recede further into the distance: by the time the chequered flag came out, Keselowski had a three second edge over Johnson and cruised over the line to take his fourth win of the season and first blood in the 2012 Chase.

By the time he spoke with reporters after the race, Johnson's initial anger over the pit exit blending had subsided, and he was realistic to admit that the better can had won: "I don't think it played an outcome in the race," he admitted. "The way he made quick work in traffic and stretched it out on me, I'm not sure I would have held him off.

Keselowski didn't see quite what the fuss was about his pit lane exit move. "There is no enforced line like you see in other sports, and that's not a bad thing," he pointed out. "That's just one more thing to monitor during the race.

"It's certainly a - I don't want to say a gentlemen's agreement - it's a policy of merging down the backstretch, off of turn 2, I think it said specifically in the driver's meeting, and I feel like that's what we did," he added. "You can make rules that count it down to the inches and just make it a pain in the [neck] for everybody that participates in the sport, or you can just have a rule like we do. And I felt like I was inside those guidelines."

NASCAR had agreed with him - something that you can be sure Johnson, the Hendrick team and indeed everyone else on pit road will note down for future reference and used - and Keselowski was celebrating in victory lane, along with car owner Roger Penske who had flown in from Fontana, California overnight following his organisation's crushing disappointment to narrowly fail to secure the IZOD IndyCar Series championship with Will Power.

"A great weekend is what I'm thinking now," said Penske of how he felt on Sunday afternoon, standing in NASCAR victory lane less than 24 hours after the Fontana let-down. He was particularly happy to have bested Hendrick Motorsports' Johnson and Kahne in such a close on-track fight: "They're the gold standard, and we want to beat them," he said.

But Keselowski was quick to manage expectations and not let everyone get carried away with this early success. "We might have won the round, but we didn't by any means knock 'em out," he warned. "We're feeling good about today, but [we] know that we have a lot of work to do."

Keselowski's lead in the Sprint Cup standings is just 3pts over Johnson, with Tony Stewart a further 5pts back after finishing a solid sixth place in Chicago despite that early problem with having a pit a second time with a vibration.

"We probably passed more cars than anybody today, so not exactly what we were looking for," admitted Stewart of his afternoon. "We were just a little bit off and we'll keep working on it, but if we can be a little bit off and end up with a top ten then we're in good shape."

Denny Hamlin is in fourth place in the Cup standings, despite a problem refuelling problem which left him with too little gas in the tank to make it to the end, causing him to drop out of the top ten all the way to 16th place in the final minutes.

"We ran out of fuel, we didn't get it all the way full on the last stop," he explained. "We made an adjustment instead of putting fuel in the car and you have to have fuel to finish."

After his third place at Chicago, Kasey Kahne is up to fifth place in the standings, 15pts adrift of Keselowski but very much right back in the thick of it: "We had a great run, the team did a really nice job," he said. "The pit stops were perfect throughout the whole race. The car was good.

Even so, it wasn't quite good enough to match the likes of Keselowski and Johnson, and Kahne wasn't happy imply being the "best of the rest".

"We battled for about three laps there through the middle part of the race, and ended up third. I think I ran third most of the race, it was a solid run for us," he said. "I was slipping a little more than I would have liked to off the corners, and we weren't able to get a handle on that. Tried to lead a lap there with Jimmie and just wasn't able to get by him."

Chase contenders Dale Earnhardt Jr., Martin Truex Jr. and Clint Bowyer all finished in the outer regions of the top ten, which keeps their Chase hopes very much alive but wasn't the explosive start to the play-offs that they had been aiming for.

Earnhardt in particular was left ruing the mistake that had forced his overnight engine change and sent him to the back for the start of the race: "I was disappointed with myself in making the mistake with the engine and getting us that far back at the start of the race. We couldn't really overcome the track position

"We had a great car at the start and first half of the race - for the first 100-130 laps we had a really fast car," he said. "We made a couple of adjustments that didn't really help us out how we needed help and we sort of made the car ordinary and just kind of had to maintain track position ... We're still in the fight, so we'll go on to the next one still with a shot."

"It just wasn't a good day," admitted Bowyer, who had come into this race voicing some very high hopes of competing for the outright win to kick off his own Chase campaign. "I don't know whether it was strategy or pit stops or what, but it seemed like we lost spots on pit road all day and it just cost us. You ain't going to win a championship with decent days -- you have to have good days," he pointed out.

"We were horrible at the start -- just straight to the rear," said Truex, Bowyer's team mate at Michael Waltrip Racing. "We were just so tight all day long. I don't know what happened, I can't believe we missed it that bad.

"We just had to stick with it, keep pushing and keep pounding on it," he continued. "We made lots and lots and lots and lots of changes -- big changes and it just worked at the end. We just kept getting them one at a time."

Kevin Harvick finished the race in 12th place just ahead of Greg Biffle, who was frustrated with the way his day had ended.

"We were really going good there at the end and we did our last stop and the car just went bad," he said. "It just got way too loose and we were hooking the bottom. I don't even really know what happened. We were driving up through there and the car was getting better and better and it never fails - the last stop of the day we put our tires on and it went bad."

Biffle's outgoing Roush Fenway Racing team mate Matt Kenseth had a shaky weekend - literally in his case, as a shock absorber fell off mid-race making the #17 a real handful on the bumpy Chicagoland Speedway race surface. He managed to hold on to it till the next round of pit stops and finished a lap down in 18th place, which might not have veen the result he'd wanted, but at least it wasn't the same-scale disaster as had befallen Jeff Gordon.

"We had a brake line get loose at Bristol and a shock fall off today so obviously we have to get to the bottom of that," said Kenseth after the race. "We didn't have a very fast car to start with ... When we had that problem, we got so far behind."

There's still time for Kenseth et al to rally back and figure in the Chase, but they can afford no further mistakes over the next nine weeks or else they might find themselves staring helplessly on as Keselowski, Johnson and Stewart pull away and make the battle for the Sprint Cup championship an increasingly private affair.

Full race results and championship standings available.