Supasundae (8-1) got the better of former Cheltenham Festival winner Faugheen in a thrilling Irish Champion Hurdle at Leopardstown.
The Willie Mullins-trained Faugheen had come into the race with plenty to prove after being pulled up last time out.
The victor, ridden by Robbie Power and trained by Jessica Harrington, ran over three miles in his last race.
But he showed plenty of speed over two miles, challenging Faugheen and overhauling the 9-10 favourite.
Faugheen, with Paul Townend on board in place of the injured Ruby Walsh, had gone out into the lead from the start but Supasundae kept tabs on his rival.
Turning for home, the pair seemed set to fight it out. However, the pace, which had been a feature of Faugheen's performance in the build-up to the 2015 Cheltenham Champion Hurdle win, was not as evident as before.
Although Faugheen jumped the last two hurdles solidly, Supasundae started to pull away and won by two and a quarter lengths.
"Coming here we wanted this to be a nice prep run for Cheltenham," said Harrington afterwards.
"It's a long time since he won over two miles but he jumped superbly and having Faugheen there really helped him.
"We will still go over three miles in the Stayers Hurdle at Cheltenham - he's not a natural speed horse and he won today because he is a stayer."
While Faugheen's owner Rich Ricci said he felt he had learned nothing new, trainer Mullins described the horse's effort as "disappointing".
"He's sort of half back on track," he said. "But he'll have to improve a lot to be back where he was."
Cornelius Lysaght, BBC horse racing correspondent
This was certainly miles better from Faugheen than when pulled up here after Christmas; he led for a long way, looking quite his old 'machine' self.
But just when you thought that he would gather steam, stride on and win in emphatic style, not a lot happened really, and he was soon booked for second.
It was the worst possible result in a way: he didn't win easily, and it wasn't disastrous, so after this there is only one thing to do, which is to keep on towards Cheltenham, not really knowing what might happen.