David Pipe and Tom Scudamore were left stunned as Western Warhorse floored Champagne Fever to cause a huge upset in the Racing Post Arkle Challenge Trophy at Cheltenham.
Champion Bumper and Supreme Novices' Hurdle winner Champagne Fever was an 11-4 joint-favourite to complete the Festival hat-trick and jumped superbly at the head of affairs under Ruby Walsh.
However, Western Warhorse tracked him into the straight under a confident Scudamore and quickened up to lead after jumping the final fence.
Champagne Fever did his best to battle back, but 33-1 shot Western Warhorse passed the post a head to the good.
Champagne Fever's fellow joint-favourite Trifolium was four lengths away in third.
With Willie Mullins having already taken the opening Supreme Novices' Hurdle with the incredibly impressive Vautour, Champagne Fever was unsurprisingly popular with punters to complete a double.
Everything appeared to be going well for most of the two-mile contest, with Champagne Fever fencing immaculately, but few would have expected the Pipe-trained Western Warhorse to still be in with a shout on the run-in and he mastered the Irish raider under a jubilant Scudamore.
Irish Arkle hero Trifolium ran well in third without being able to match the front two after the final obstacle.
The major disappointment of the race was 2012 Champion Hurdle hero Rock On Ruby, runner-up behind Hurricane Fly in last year's Champion.
He made a shuddering error at the third fence and Noel Fehily did remarkably well to keep the partnership intact.
However, he was soon back-pedalling and never looked likely to land a telling blow.
Pipe said: "He's been point-to-pointing in Ireland and jumped well at Doncaster, so even though he'd only had one run over fences, it wasn't a real worry.
"What happened at Kempton when he dumped Tom Scudamore may have been a blessing.
"Roger (Brookhouse, owner) wanted to run him in this, but I wanted to go for a nice handicap somewhere, so it's a good job Roger got his way.
"He's always shown lots of ability and the drop back in trip has suited.
"Tom has given him a really canny ride, because I told him to bounce out and make the running, but they were going a stride too quick, so he just dropped in."
Scudamore said: "I still can't quite believe that. I've won an Arkle, it's extraordinary.
"It was Roger Brookhouse who said drop him back to two miles.
"We were not expecting that. It's a great thrill and for a change I'm lost for words."
Mullins said of Champagne Fever: "He's run a fantastic race.
"You'd be disappointed with the result, but not the performance. That's it for two miles. We'll step him up in trip next season."
Charles Byrnes, responsible for the third home, Trifolium, said: "He's run a very honest race.
"He could never quite get to Champagne Fever at the second-last, but I'm thrilled with his attitude."