Azertyuiop took advantage of pre-race favourite Moscow Flyer's fall to win the Queen Mother Champion Chase.
Ruby Walsh's mount went from strength to strength to finish nine lengths clear of Flagship Uberalles in second while Tony McCoy's Tiutchev was third.
Moscow Flyer was looking in fine form, but a slight misjudgement at the fourth from last fence saw the horse send jockey Barry Geraghty flying.
In a field of eight, Cenkos finished back in fourth.
Walsh said he was unaware of his rival's misfortune at the fence.
"I looked back down the hill and I couldn't see Barry (Geraghty) and I wondered where he had gone," said Walsh.
"I had a super ride, settled great and I'm just delighted he's won.
Walsh said the win in the prestigious race was a boost after his falls on Thisthatandtother on Tuesday and Mossy Green on Wednesday.
"I've been looking for this for so long. I know I'm still alive and kicking now, but it hasn't been the best day and a half I've had."
Geraghty was bitterly disappointed after coming off his horse.
"Moscow Flyer galloped down to it and met it long," said Geraghty.
"I was just sitting on him and gave him a squeeze and he paddled into it, as a horse can do when you're travelling at that speed.
"It's a pity, but the horse is okay and so am I."
Azertyuiop's trainer Paul Nicholls was delighted with his horse's performance, but conceded he would rather Moscow Flyer had finished the race.
"It was a shame for Moscow Flyer," he said. "We'll never know what the result would have been.
"We felt Azertyuiop would take a lot of beating. He's a horse who puts a lot into his racing."
Azertyuiop has already been quoted at 5-2 for a repeat victory next year, with Moscow Flyer a 7-2 chance.
Rule Supreme landed the Royal & SunAlliance Chase, with hot favourite Our Vic
managing only third.
The Irish-trained winner, who came in at 25-1, powered up the hill to beat Royal Emperor by a
length and a quarter, with the 11-8 favourite two lengths away.
The result came as no surprise to winning trainer Willie Mullins.
"He ran a cracker in the Thyestes at Gowran Park when he finished third after a bad mistake, and that run alone gave him an outstanding chance.
"He's done some serious work, this horse. Jumping has always been the problem and David knew what he had to do," he said.
Racegoers were treated to an exciting opener when Fundamentalist gamely held off the late challenge of the 7-4 favourite, Inglis Drever, in the Royal & SunAlliance Novices' Hurdle.
Philip Hobbs, who had supplied the runner-up in both the Smurfit Champion Hurdle and the Queen Mother Champion Chase, enjoyed a welcome change of luck with Monkerhostin's win in the Coral Cup.
Timmy Murphy took his second winner of the Festival when coming fast and late on Tikram to land the Mildmay Of Flete Challenge Cup to give Brighton trainer
Gary Moore his first Festival success.