Jimmie Johnson claimed pole position for this weekend's NASCAR Sprint Cup race, and it comes at a critical point of the championship with just four races remaining to decide the title before the end of the 2012 season.

"We've helped ourselves out dramatically today by qualifying on the pole," the five-time champion agreed after securing the lead spot for the start of Sunday's Tums Fast Relief 500 Cup race. "We've got the safest pit stall, and starting with track position is very important.

"But you've still got to go run the race," he cautioned. "When the playoffs hit, it doesn't matter what sport it is, crazy things happen ... You never know. It's going to be a long race."

Even more crucially, his main rival for the Sprint Cup - Penske Racing's Brad Keselowski, who leads the championship by seven points over Johnson coming into Martinsville - slumped to a potentially disastrous 32nd pot on the starting grid.

"I don't enjoy qualifying like crap," said Keselowski after his disappointing time trial on Friday afternoon. "That's not what I come to the track to do, but it's been the course of late."

The concern for Keselowski is that the half-mile oval make it difficult to gain ground, while all the time the leaders are charging up close form behind and could possibly put Keselowski's #2 a lap down if there is a decent green flag stint to open the race with on Sunday.

Keselowski, naturally, was choosing to ignore that dire possibility and instead looked for silver linings to the qualifying gloom: "We take solace in the fact that in the actual racing my team has done a good job on all levels, that's what we have that's going right," he said. "I feel confident it will work its way out. It's a very long race with 500 laps around here. There's a lot of tools in our tool chest to help us recover."

All things considered, then, Johnson wouldn't be sincere if he pretended not to be thinking that this weekend presented a golden opportunity to make a decisive break for the front of the Chase at just the right moment.

"I feel really good about my Lowe's Chevrolet and I think we'll be in strong, championship-form leaving here," he admitted. "When the playoffs hit, it doesn't matter what sport it is, crazy things happen. And with that being said, yeah, we come here thinking that we should be able to get some points on the #2."

Of course, it's not just Keselowski that Johnson has to be wary of at this stage of the title battle: Denny Hamlin, Clint Bowyer and Kasey Kahne are all still firmly in the hunt, especially if current points leader Keselowski falter at the front.

Hamlin will start from fifth place in the #11 Joe Gibbs Racing car, while Clint Bowyer will be a factor starting from eighth position on the grid in the #15 Michael Waltrip Racing machine. Johnson's Hendrick Motorsports team mate Kasey Kahne has made things slightly harder for himself after only managing a 15th place starting spot.

"The car was pretty good I was just a little bit tight, just didn't turn the centre of the corner quite as strong as I would have liked," said Kahne. "The car still felt really good," he insisted.

Johnson's title campaign is helped by the fact that the rest of the first two rows on the grid are all non-Chase contenders: Brian Vickers starts alongside Johnson on the front row as he takes over the #55 from Mark Martin this weekend in a car-sharing deal that was confirmed on Friday as being extended into 2013, with Kyle Busch and Jeff Burton lining up on the second row.

Aside from Hamlin and Bowyer, the other Chase contenders in the top ten are Matt Kenseth coming off his win last weekend at Kansas with sixth place on the grid at Martinsville, followed by reigning Cup champion Tony Stewart in seventh who said that he was relying on a change in the weather and better race pace to allow him to feature on Sunday.

"I think it's supposed to get cooler the rest of the weekend," said Stewart. "We had a decent practice - I think we made gains right at the end of our race runs before we switched over to qualifying. So we'll see. I think we'll definitely get a lot of use out of the two practices tomorrow."

Jeff Gordon and Martin Truex Jr. just miss the top ten and start alongside one another on row six, while Dale Earnhardt Jr. put the #88 into 20th place on his return from a two-race absence due to a double concussion.

Earnhardt said that he felt absolutely fine on his return to competition this weekend: "I felt like I could race at Kansas for sure, probably ran at Charlotte with no problem," he said. "I felt kind of foolish sitting at home and feeling OK and not being in the car. If the doctors said it's OK, I wanted to be in the car.

"It was really hard to see your car running around without you in it, so that was difficult," he added, before insisting that he had no regrets about seeking medical advice when he did even if it ended his 2012 Chase hopes.

"The one thing I can tell you is I'm definitely going to be honest with myself and honest with the doctors and I'm going to do whatever they tell me to," he said. "I want to be able to live a full life and not have any issues down the road.

"I feel fortunate to have recovered from this concussion quickly, and I feel lucky I made the choices I did," he added. "Had I tried to push through it like I did the other ones I was putting myself in a lot of danger."

Earnhardt's place behind the wheel of the #88 was taken by Regan Smith at Charlotte and Kansas, and Earnhardt has shown his appreciation by signing Smith to a full-season seat with his JR Motorsports Nationwide Series team in 2013. However, Smith finds himself watching from the sidelines at Martinsville, as he is without a ride this weekend and next as Phoenix Racing replaced him in the #51 with AJ Allmendinger in a game of musical race seats. On the plus side, Smith has been told he'll take over the #51 for the final two races of the year at Phoenix and Homestead.

"Part of me was like, 'I don't want to go to the race track if I'm not in the car,'" Smith revealed. "And then the other part of me was like, 'You know, there's still something I can learn.'

"So I'll be here on Sunday and watch from the roof, listen and scan people, scan different cars and make the most out of it to continue to better myself as a driver," he said, adding that he didn't see a return to Nationwide - where he last competed in 2007 - as a step back or a setback in his career.

"I'm getting into a situation where we feel like we're going to win races and contend for a championship," he insisted. "To me, that means more than anything, as a driver. That's what we do. That's why we want to be race car drivers -- to win the trophies and stand on top of the car and celebrate with our guys after the races."

Meanwhile AJ Allmendinger qualified the Phoenix Racing car in 26th place on Friday, although he admitted that it hadn't been a particularly strong performance.

"We struggled today a little bit," he said. "The whole day has been kind of messed up. We have really been struggling with some brake trouble ... I think in race trim, it's not as bad as the outright speed in qualifying trim. We'll just keep working hard.

"We've got two practices tomorrow," he added. "I started 29th here in the first race here [earlier in 2012] and finished second so we will be all right and good to go."

Full qualifying and Friday practice times are available.