Saint Roi came from last to first to win the Brand New Racing Post App Novice Chase on the opening day of the Leopardstown Christmas Festival.
The JP McManus-owned seven-year-old finished ahead of Visionarian and 8-11 favourite Fil Dor.
Saint Roi’s win came after finishing second to Fil Dor on his chasing debut at Navan in November.
“I thought he ran very well against a horse that had already had a run in Navan,” said trainer Willie Mullins.
“If he’d won we’d be coming here anyway so rather than running in another beginners chase, I thought let him have a crack at a good prize.”
Fourth in the Irish Champion Hurdle, the Champion Hurdle at Cheltenham and the Punchestown Champion Hurdle last season, 3-1 shot Saint Roi dominated the betting with Fil Dor.
Visionarian gave a bold sight in front for much of the Grade One contest, with a couple of jumping mistakes late in the back straight putting Fil Dor on the back foot.
Mark Walsh bided his time on Saint Roi before challenging for the lead as they approached the final fence.
Visionarian, a 25-1 outsider, tried to hold on but Saint Roi’s class shone through as he finished two-and-a-quarter lengths ahead.
“He jumps well enough and he’d schooled very well in the meantime,” Mullins added.
“We decided to change the tactics. JP was wondering would he be better waited with and Mark agreed. He’s a nice prospect for the rest of the season.
“He’s not the biggest horse in the world but he jumps very efficiently. He’s also a lot more sensible over a fence than a hurdle.
“He had a hurdle rating good enough to run in championship races but was probably not a champion hurdler himself.”