Trainer Colin Tizzard registered his sixth victory at The Festival overall and first of 2018 with Kilbricken Storm's 33/1 success in the G1 Albert Bartlett Novices' Hurdle over three miles.
Ridden by Harry Cobden, the seven-year-old son of Oscar quickened up well after the final flight to master long-time leader Fabulous Saga, who faded rapidly out of contention thereafter, to score by three lengths.
Nicky Henderson's OK Corral (16/1) stayed on well to finish second, with stable companion Santini, the well-supported 11/4 favourite, a further half-length back in third.
Harry Cobden salutes on Kilbricken Storm
A delighted Tizzard said: "It was a smashing performance from Kilbricken Storm.
"He has had pus in his foot - his shoe off and on - and it's unreal to win like that - it didn't stop him!
"He was a 20-grander at the sales. I went to the sales last night and horses were making so much money, I was thinking that we weren't going to have a winner here, and the next one has won. It's what National Hunt racing is for and it's fantastic.
"He had a bit of a dirty nose a week after he ran in the Challow but I never knew he was going to be that good even when he was dead right.
"He just appeared to travel really well. He was fifth or sixth and moved into it. Then we were waiting for the cavalry to come and they didn't.
"We've seen it all week that the ones in front have been caught, but he wasn't today."
After Bridget Andrews's victory on Mohaayed it was the turn of Harry Cobden, 19, on the Colin Tizzard-trained Kilbricken Storm, who won the three-mile G1 Albert Bartlett Novices' Hurdle. The winner (33/1) beat the Nicky Henderson pair OK Corral (16/1) and Santini (11/4f) by three lengths and one and a half lengths.
Cobden said: "It is very testing conditions and I tried to keep him wide to find a little bit of better ground. I wasn't sure if I was doing the right thing, but the horse jumped and travelled and won nicely. A great day all round.
"I didn't want to commit too early [to close down long-lead pacesetter Fabulous Saga] and was half thinking, 'Do I chase this one and risk going too early', but thankfully my horse was brave and tough and fought on.
"This is only my third Festival and I've never encountered conditions quite so testing. I started the week with 10 rides, two were withdrawn and I've had two thirds - I was thinking, 'That's me done', because I didn't think this lad could win, but he proved me wrong.
"He's had a few little issues and Colin was trotting him up this morning to make sure he was okay, and thankfully the vets said he was fine to run. When the adrenalin is up you don't feel it - if I had a bad toenail I wouldn't be thinking about it out there.
"This is right up there with the two Grade Ones I've won on Politologue and Irving. My father, Will, is here watching and looking shocked - I don't think he backed me."
2.50pm Albert Bartlett Novices' Hurdle (Grade 1)
1 KILBRICKEN STORM (A Selway & P Wavish) Colin Tizzard 7-11-05 Harry Cobden 33/1
2 OK CORRAL (JP McManus) Nicky Henderson 8-11-05 Barry Geraghty 16/1
3 SANTINI (Richard & Lizzie Kelvin-Hughes) Nicky Henderson 6-11-05 Nico de Boinville 11/4 fav
Distances: 3, 1½
Tote Win: £45.30 Places: £10.70, £4.50, £1.90 Exacta: £721.20
Colin Tizzard - 6th winner at The Festival
Harry Cobden - 1st winner at The Festival