Cheltenham runner-up Sir Des Champs held off a late challenge by Long Run to win the Gold Cup at Punchestown.
With Davy Russell back on board, the Willie Mullins-trained seven-year-old just managed to justify his status as 2-1 favourite.
Long Run finished strongly under Sam Waley-Cohen, while Bob Cooper's mount First Lieutenant was third.
For Mullins, the victory was his first at the race since Florida Pearl took the spoils in 2002.
"It was a great performance," said Mullins. "Davy gave him an enterprising ride. He grabbed the bull by the horns at the third last.
"I thought he might have come unstuck at the last, but the horse came again. He jumped well."
Russell, about to retain the Irish jump jockey championship, made a positive move down the back straight, taking up the running off Long Run at the third-last and going two lengths clear.
There was not much between Sir Des Champs and Long Run at Cheltenham and yet again the pair proved they were closely matched.
Over on the far side, First Lieutenant, a winner at Aintree, also had a chance, but Sir Des Champs held on by three-quarters of a length, the placings unaltered following a stewards' inquiry.
Russell was not able to ride Sir Des Champs at Cheltenham because of injury and was replaced by Tony McCoy.
Meanwhile, Mullins will be hoping to be back in the winner's enclosure again on Thursday as Quevega goes for a World Series Hurdle hat-trick.
The chief competition could come from Solwhit, trained by Charles Byrnes.
A winner of six Grade One prizes before being sidelined by injury, the nine-year-old has returned with victories in the World Hurdle at Cheltenham and in the Liverpool Hurdle at Aintree.
Mullins also saddles Zaidpour and Fiveforthree in the seven-strong field.
Jonjo O'Neill's Holywell and the Nick Williams-trained Reve De Sivola travel from England, while Oliver McKiernan's Whatuthink completes the line-up.