Un De Sceaux saw off stable companion Douvan to claim victory in the BoyleSports Champion Chase at Punchestown.
Trainer Willie Mullins saddled four of the nine runners in the two-mile Grade One, with Douvan the 4-5 favourite under Paul Townend.
However, the admirable Un De Sceaux, ridden by the trainer’s son, Patrick, fenced fluently out in front and passed the post two and three-quarters of a length ahead of the odds-on market leader.
A Toi Phil finished third, but was another seven lengths adrift at the line.
Patrick Mullins said: “I’ve been dreaming about riding that horse. When I was told I was riding him I was like Charlie when he got the golden ticket off Willie Wonka!
“I schooled him yesterday and even schooling him was some buzz.
“It took him a while to warm up into the race. He didn’t jump or travel like he can and I was a little worried, but I think that was just the good ground.
“Once he’d warmed up I just let him at it and he runs horses into the ground. Realistically I didn’t think he was going to beat Douvan or Min on this ground over this trip, but he’s a horse that always runs well, so you can never count him out.”
Willie Mullins said: “It was a terrific race. I felt looking at the horse that he wasn’t going at all for the first half.
“Coming past the stands I thought he was on the wrong leg and he wasn’t galloping the way he normally does.
“Patrick felt the same riding him and he said he just pinged the first one down the back and he just started to gallop.
“It was a hell of a performance to come out after Cheltenham and then Fairyhouse and then here . Anyone doubting him at Fairyhouse got their answer today anyway.”
On Douvan, the County Carlow handler added: “I think Paul (Townend) probably thought at that stage that he might have enough in the tank, but when he moved on his fellow he was disappointed, but Un De Sceaux is no back-number.
“Paul just felt when he had to go to the other fellow he didn’t lengthen his stride and didn’t seem to be in that form. Something might come up because of that.