Garry Ringrose scored a hat-trick as last season's runners-up Leinster beat Benetton 33-19 and Clermont Auvergne thrashed Harlequins in the European Champions Cup on Saturday.
Leinster were beaten by Saracens in the final in May, but the 2018 Champions Cup holders started their quest to regain the trophy with a bonus-point Pool 1 win at the RDS Arena.
Ringrose was the star of the show, the Ireland centre crossing twice inside the first 14 minutes and completing his treble after the break.
Ronan Kelleher also touched down on his European debut before Johnny Sexton rounded off a slick move early in the second half, the Ireland fly-half also adding six points with the boot.
Tries from Dean Budd, Epalahame Faiva and Luca Sperandio were in vain as Benetton were second best in the all-Pro 14 encounter.
Challenge Cup holders Clermont hammered Quins 53-21 in the Pool 2 clash at Stade Marcel Michelin.
Alivereti Raka and Peceli Yato grabbed doubles as the Top 14 side scored seven tries, blowing Paul Gustard's side away.
John Cooney made amends for an incredible missed penalty by slotting over the winning points from the tee to give Ulster a 17-16 success in the other Pool 2 match at Bath.
Exeter Chiefs are the early Pool 2 leaders following a 31-12 bonus-point win at La Rochelle, while DTH Van Der Merwe scored Glasgow Warriors' only try in a 13-7 home triumph over Sale Sharks.
Munster opened their European campaign with a 32-13 Pool 4 defeat of the Ospreys on their travels, Keith Earls and Andrew Conway among their four try-scorers.