Sizing Europe recovered from his Cheltenham Festival defeat to win the Champion Chase on the opening day of the big Punchestown meeting.
The 10-year-old lost his Queen Mother Champion Chase title last month when beaten by Finian's Rainbow.
However, he had two-and-a-quarter lengths to spare from Realt Dubh on Tuesday in testing ground.
Cheltenham Gold Cup prospect Sir Des Champs survived a final-fence scare to win the Novice Chase.
Willie Mullins' horse, ante-post favourite for next year's Gold Cup, led by four lengths heading into the last but he very nearly unseated jockey Davy Russell before clinching a 36-length victory as his nearest challengers Mossey Joe and Frisco Depot both fell.
Sizing Europe had suffered his Cheltenham Festival defeat after both he and Finian's Rainbow were forced to bypass the last fence after an earlier fall.
After China Rock led early on in Tuesday's Punchestown race, Sizing Europe moved into the lead after the fourth last and while Realt Dubh, with Paul Carberry on board, threatened on the run-in, Andrew Lynch guided Henry de Bromhead's horse to victory.
Last year's winner Big Zeb was some distance back in third place.
"He was super," said winning trainer De Bromhead after his horse's fifth Grade One victory over fences.
"I was just getting a bit worried that we were going to be caught but we're delighted."
Sir Des Champs stretched his unbeaten run to seven races since joining the Willie Mullins stable with his Novice Chase win but his struggles at the last in the moderate field despite the race's Grade One status will be a concern for his backers.
The six-year-old was sent off the 2-7 favourite following a superb performance in the Novices' Chase at Cheltenham, and was stepping up to Grade One level for the first time.
With Mossey Joe suffering a horrible fall at the same fence when running a big race, hampering Frisco Depot who unseated his rider, Sir Des Champs came home 36 lengths ahead of Shop DJ.
Meanwhile, Philip Hobbs produced a superb training performance as his Snap Tie returned from over 900 days off the track to land the handicap hurdle on day one at Punchestown.
The 10-year-old had last been seen winning a Cheltenham novice chase in October 2009 and Hobbs had gradually nursed his charge back to fitness.
Richard Johnson was never too far off the pace on the 16-1 chance and his task was made easier when strong travelling joint-favourite Ceol Rua slipped up on the flat before the turn for home.
Benash emerged as the only serious threat to the British raider in the straight, but Snap Tie kept pulling out more to register a two-length victory.
1. Sizing Europe (A E Lynch) 8-13 Fav
2. Realt Dubh (P Carberry) 6-1
3. Big Zeb (R M Power) 13-2
4. China Rock (R Walsh) 18-1
1. Sir Des Champs (D N Russell) 2-7 Fav
2. Shop DJ (A P Crowe) 18-1
3. Ordinary Man (J R Barry) 33-1