Defending champion Jamie Whincup served notice upon his closest V8 Supercar Championship rivals by setting quickest time in the dying moments of today's practice sessions in the lead up to this weekend's Big Pond 300, the penultimate event in the title chase.

Held over three separate sessions, Whincup's last gasp effort deposed Fabian Coulthard and early pace setter James Courtney. Ironically, the respective TeamVodafone, Wilson Security Racing and Jim Beam Racing trio of drivers were all driving chassis supplied by Triple Eight Engineering although, conversely, using three different sources for their engines.

The Toll-Holden Racing Team pairing of Will Davison and Garth Tander, holding down second and third in the point standings, registered fourth and 15th fastest times; much of which could be attributed to a succession of red-flag interruptions and lack of suitable practice rubber. With today's unrestricted use of control tyres, many of the quicker laps were set in the closing stages as more adhesion went down onto the abrasive surface.

Visits into the expansive sand bunkers surrounding the circuit were many, and included Whincup, team mate Craig Lowndes, Lee Holdsworth and both Jason and Steven Richards.

Courtney had set the benchmark with an impressive time until he suffered a split power steering line which compelled him to sit out the latter half of the second session and some of the final one whilst repairs were undertaken.

"We lost a lot of time while the boys in the crew bled the brake lines to prevent an air lock," said Courtney, "The car was quite good from the time it rolled out of the truck and we only made a slight suspension change at the end as we're happy with the way that it is looking after its tyres.

"You'd think that Jamie would back off and think about leading the championship but he rarely makes mistakes. We may have the same chassis as he does but we've all got completely different set-ups; we've also got a competitive engine package as there isn't a lot between us in power but that might be different in fuel economy."

Kiwi Coulthard was pleased to be second given he is keen to give a result to the team he leaves after the next and final round.

"It wasn't a clear lap by any means as I had to deal with lapped traffic," the Kiwi said, "We've been quick all day and I expected to be near the front. My guys have been putting in some long hard hours burning the candle at both ends to make up for some mistakes I've made recently, but the morale is high as we want to finish off doing the best we can. My goal all year has been to win a race and so far I've managed a podium as it is very hard to do."

For Whincup, however, the defence of his Championship won't be secure until Davison is mathematically defeated.

"It is great to be quickest, but it is a bit artificial given the red flags and the fact that not everybody had a run on fresh rubber," he explained, "I'm not jumping to conclusions as I only really got one quick lap in, but I'm not going to be cautious as, while the margin is still less than 150 points, one mishap could change everything."

A surprise seventh quickest was Jack Perkins, who was as high as second until a minute left to run.

"After all the disappointments of the endurance races, I still have three-and-a-half sets of green tyres left," he noted, "At least now I've had a chance to know how far to push when it comes to qualifying tomorrow."

Behind the top three ran Davison, FPR duo Richards and Mark Winterbottom, Perkins, Jason Bright, Cameron McConville and Todd Kelly. Much interest will surround the compulsory use of a set of 'soft' tyres which have to be run at least once in the race/s as, tactically; it will introduce another element into the mix given its expected short life expectancy.

Sitting second on the Championship points table, Davison put all his effort into tuning the #22 Commodore before tomorrow's qualifying sessions, pushing the car to its limits. He managed the eleventh fastest time in the second 50-minute session, but was able to improve on that in the third.

"The car was pretty good straight out of the truck, we probably only needed to fine tune it but we were searching for a direction, so we made quite a lot of big changes just to find out what it was like," he reported, "The track's very slippery, but we had a productive session.

"It's hard to find a nice balance, but we only had one lap at the end on a better set of tyres and ended up fourth. Jamie's very quick, but I wouldn't be surprised if he had brand new tyres on - all will be revealed tomorrow. I'm pretty happy with my car, we didn't have it 100 per cent, but from what we learnt I think we can put it to good use for tomorrow."