Master Minded dug deep to hold off the fast-finishing Somersby
Master Minded just held on by a short head under Tony McCoy to win the Victor Chandler Chase at Ascot from Somersby.
The dual champion chaser, trained by Paul Nicholls, was sent off 4-7 favourite and looked relatively untroubled until the latter stages.
Henrietta Knight's 8-1 chance Somersby put in a stirring late challenge, but McCoy just held on, with Mad Max third.
Master Minded is owned by Clive Smith, like Kauto Star who lost for McCoy in the King George a week earlier.
The 15-time champion jockey was critical of his own ride at Ascot afterwards, feeling it may have contributed to his mount tiring near the end in testing ground.
"He did well to win, they went a real good gallop early on and at Swinley Bottom he came back on the bridle and I let him run when I shouldn't have done," said the BBC Sports Personality of the Year.
Nicholls said: "I'm relieved. I was disappointed initially because turning in I thought he was going to go away and win quite nice and then I was thinking something obviously isn't quite right.
"I just said that to AP [McCoy] but he wasn't having any of that, he just said he gave him a bad ride - his words not mine."
Kauto Star had finished third to winner Long Run when bidding for a fifth straight King George VI Chase triumph at Kempton, and was later found to have an infection.
Smith indicated the dual Gold Cup winner might be better suited by his regular partner Ruby Walsh, who is out injured, while Nicholls has had to cope with suggestions his yard have been under a cloud.
"I've been under a bit of pressure this week with one thing or another as some haven't run as well as they can so it's nice to have a winner," said the champion trainer.
Of Master Minded, he added: "The runner-up is a good horse and we are probably not in the best of form. In the spring it will be totally different.
"AP is kicking himself because he said if he'd got beat he wouldn't have forgiven himself.
"They can't always run to their very best, we saw that last week, and I've got to get him back to his very best.
"He travels brilliantly and jumps well. Don't forget he's had a breathing operation in the summer and no horse with a breathing issue wants this ground.
"Come the spring, with the horses in better form, he'll be there again."
Victory in the two mile, one furlong contest was eight-year-old Master Minded's third win of the season, his seventh Grade One success and took the French-bred's career earnings past £1m.
He remains favourite with most bookmakers, albeit eased from about 7-4 to 5-2, to win a third Queen Mother Champion Chase at the Cheltenham Festival on 16 March.
The 2010 winner Big Zeb is 3-1, with Master Minded's stablemate Woolcombe Folly 8-1, ahead of Arkle Chase winner Sizing Europe (11-1) and Somersby (12-1).
Master Minded and Somersby finished 20 lengths clear of Mad Max, with Kalahari King unlucky in running as he finished a creditable fourth on his return.
Somersby's trainer Henrietta Knight said she was undecided whether to run the Arkle Chase runner-up in the Champion Chase over two miles or the Ryanair Chase (2m 5f) at Cheltenham.
Meanwhile, the Nicky Henderson-trained Grandouet is now a clear favourite for the Triumph Hurdle after a six-length win earlier on the Ascot card.
Victor Chandler Chase, Ascot, 2m 1f
1 Master Minded (Paul Nicholls) Tony McCoy 4-7 fav
2 Somersby 8-1
3 Mad Max 8-1
9 ran. Dist: Short head, 20 lengths