Holden Racing Team's James Courtney admits his '110% commitment' through turn eight was a key factor in sustaining his lead ahead of Red Bull's Jamie Whincup during the second Clipsal 500 race.

Courtney and Whincup spent the entire 39-lap nose-to-tail after the factory Holden driver gained the high ground over the Triple Eight man at the beginning of the race.

The pair quickly pounced upon race leader Chaz Mostert shortly after the second safety car phase where the battle for position intensified that bit further.

As the race progressed, a clear pattern emerged with Whincup's Holden seemingly able to draw dangerously close to Courtney into the braking area's while the HRT Commodore hit back through the high speed corners.

With little over a car length separating the two on a grandstand final lap, Courtney and Whincup left nothing on the table, displaying a heroic level of commitment through turn eight - the race winner says that was the difference between winning and losing.

"The second race was a really tough today particularly against Jamie. He is a fierce competitor and he didn't give me an inch," said Courtney.

"It was a good hard race and I really had to earn that one. I had to try and not make any mistakes because if I made the slightest one he would have been down there."

"I had to be 110% committed through turn 8 every time to get enough of a margin so I didn't get passed into turn 9. Anytime you beat these guys it's a good race, so to finish in front is a good feeling."

"The car was acting quite different on both sets of tyres and I produced some pretty good racing today I think. Although I hit the tyre bundle at turn 1 with probably three laps to go and I was on the radio to the boys asking if they could see the front bar hanging off or if it was still on."