Lisnagar Oscar won the Paddy Power Stayers' Hurdle at 50/1 as odds-on favourite and reigning champion Paisley Park finished out of the frame.
The 2019 hero and dominant force in the staying division, Paisley Park finished weakly up the hill, ending up seventh as victory went to the Rebecca Curtis-trained outsider Lisnagar Oscar, who was third to Emma Lavelle's favourite in the Cleeve Hurdle when they met earlier in the year.
He could be spotted moving noticeably well as the field closed the gap on long-time leader Apple's Jade and jockey Adam Wedge guided him over the final flight and up the climb to the line to score by two lengths from 20/1 chance Ronald Pump, with the strong-travelling Bacardys (33/1) back in third.
The race was teed up by a free-going Apple's Jade under champion jockey Richard Johnson and the winner clearly relished the thorough test of stamina, sweeping down the outside and closing in on Apple's Jade on the turn for home.
He took it up on straightening for home, where Summerville Boy and the quietly-ridden Emitom also holding chances as Ronald Pump mounted his challenge between horses.
Wedge still hadn't gone for everything on Lisnagar Oscar coming to the last, where he was neat and the runner-up less so, and he drew clear in game fashion on the run-in.
The Willie Mullins-trained Bacardys got the better of Emitom for third with Summerville Boy a close fifth ahead of last year's Pertemps Final runner-up Tobefair.
Curits, recording her fifth Festival success, said: "It's a shock he's won. I didn't think he'd beat Paisley Park, but I was hoping we'd have a good run here after the last time. It was like he'd just got his confidence back the last time. I'm just speechless.
"He was so well at home and I thought 50-1 was a massive price.
"Last year he had very good form as a novice. I thought he'd make a lovely chaser, but he didn't take to fences. He's quite small and is quick and neat over his hurdles.
"We tried fences early in the season. It all went wrong. Whether that put him off racing for a bit, I don't know. Something just wasn't quite right with him.
"He had Grade Three ulcers. Whether that has made a massive difference, I don't know. He just sprung to form six weeks ago and we fancied him to run well today."
Curtis has only recently had a baby girl, named Reeva, and added: "I had a cesarean and had a couple of weeks to recover, then I was straight back on it, as I hate sitting home doing nothing and I was straight back at the yard. You can't have time off running a yard. You just get on with it.
"It is absolutely amazing at a time when I need it, as I'm just trying to rebuild the yard. We've had four winners here before, but it has been five years, so it is just great to have another one.
"He (Wedge) is brilliant, such a solid jockey, so I'm delighted for him as it's his first Festival win."
Wedge said: "Unbelievable, it's fantastic. The little horse has tried his heart out. I couldn't believe it when I hit the front, I was just praying he'd keep galloping - he fought like a little lion up that hill."
Last year's winner Paisley Park looked to be in trouble some way out and faded late on.
His trainer Emma Lavelle said: "We're massively disappointed, but it's just one of those things - they're not machines. He's such a gorgeous horse and he's come back absolutely fine. He's been amazing horse for us who has done amazing things and I'm sure he'll do amazing things again.
"It's a shame it didn't happen today. I never really felt he was alive during the race - he just looked to be going through the motions, rather than tanking through the race as he has been doing, and his jumping wasn't quite as slick.
"It's dead old ground out there and that probably doesn't play to his strengths. He's lost two shoes - I think they were probably just suctioned off by the ground while he was running! I'm delighted for Adam Wedge, who rides a lot for us."
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