The well-backed 9-2 favourite went with Stellar Notion and Fletchers Flyer as the three moved clear from some way out, but was travelling easily the best and took up the running before the straight.
Power, who landed the Cheltenham Gold Cup on Harrington's Sizing John, still appeared to have plenty up his sleeve and after safely negotiating the last two, Our Duke powered clear to beat last year's runner-up Bless The Wings by 14 lengths.
Project Bluebook (9-2) came out best in a three-way battle for the Avoca Dunboyne Juvenile Hurdle to claim Grade Two honours for John Quinn.
Slowmotion won that race for Joseph O'Brien last year and was back on the scoresheet again, this time in the Farmhouse Foods John & Chich Fowler Memorial EBF Mares Chase as the 13-8 favourite.
The Willie Mullins-trained Diakali demolished his rivals in the Rathbarry & Glenview Studs Hurdle.
Ruby Walsh went to the front on the 9-4 chance after the first and controlled matters from that point, beating Stars Over The Sea by 20 lengths, with Jezki a very disappointing last of five.
Mullins' Renneti was on his best behaviour to run out an emphatic winner of the Grade Two Keelings Irish Strawberry Hurdle.
Walsh allowed the 5-2 chance, who can give trouble at the start, to take up the running after jumping four out and although De Plotting Shed tried to rally, Renneti eased away again to pass the post with nine lengths in hand.
Samcro landed the odds in the Ryans Cleaning Event Specialists Flat Race, while White Arm won the Fred Kenny Lifetime Service To Racing Handicap Chase and Showem Silver took the Fairyhouse Steel Handicap Hurdle.