Sprinter Sacre consolidated his position as general second-favourite for the Queen Mother Champion Chase with victory at Kempton.
But Nicky Henderson's nine-year-old had to dig deep to win the williamhill.com Desert Orchid Chase, which the Seven Barrows trainer described as "the hardest race he's had."
One interesting point after Nico de Boinville had rousted Sprinter Sacre to a three-quarters of a length triumph over Sire De Grugy was the variation in prices given out for the winner at Cheltenham, on a day when Un De Sceaux crashed out at Leopardstown.
Hills left him unchanged at 3-1, Coral eased him a full point to 9-2, making Un De Sceaux 6-4 and cutting Sire De Grugy from 11-1 into 8s.
De Boinville brought 8-11 hotpot Sprinter Sacre around the outside of both Sire De Grugy and Vibrato Valtat turning into the straight.
Approaching the final fence the favourite was locked in combat and level with his main rival, but Sire De Grugy's mistake handed the initiative back to Sprinter Sacre, who was then always holding his rival.
Henderson said: "I got the feeling that two miles round here isn't enough of a test for him and would have to say that's probably the hardest race he's had. He had to be a different horse, and a brave one, to win today, and he's won it with his heart today because his heart had to be big."
Henderson confessed to having "a few sleepless nights" ahead of his former champion's return to the venue where a heart problem affected him and caused him to pull up the season before last.
He added: "It's all a step forward, but an entirely different step. The other horse looked to be getting the better of it, but the way he's kept on you'd have to say there wasn't a lot wrong.
"There was the 'coming back to Kempton' thing, but he certainly hasn't remembered what happened and Nico's given him a lovely ride."
Henderson's immediate reaction about a plan for 2016 was to dodge the Newbury trial in February.
He said: "The one thing I wouldn't want to do is look at the Game Spirit on heavy ground. The options aren't exactly staring us in the face, and I'm not worried if he doesn't have another run (before Cheltenham).
"He's not what he was two years ago, but those are two very good performances he's put up so far this year.
"Those two years in the wilderness were very tough, you've got this great horse but you can't use it and appreciate it, and the fact he has got back to here - the reception is spectacular. He knows it and I hope he enjoys it. They do understand.
"There's a long way to go (to win another Champion Chase) and you can see Un De Sceaux bowling along coming down that hill, it won't be easy but it's what we've got to aim at, and dream about."
Gary Moore was delighted with Sire De Grugy, and said: "He's put up a great performance on ground that wasn't ideal. I'm looking forward to taking him to the Clarence House now (Ascot on January 23) and then to the Queen Mother."