Ulster and the Ospreys made short work of Newport Gwent Dragons and Zebre respectively, but Leinster looked laboured as they downed Benetton Treviso
Ulster ran in five tries as they came from behind to open their Pro12 campaign with a comprehensive 29-8 win over Newport Gwent Dragons.
The Welsh side established an early 8-0 lead courtesy of a try from debutant Pat Howard and a penalty from fellow new recruit, Nick Macleod.
But tries from replacement Robert Lyttle and wing Jacob Stockdale put Les Kiss' men in front by the interval and they then ran away with the game in the second half.
Lyttle claimed a second try and Ruan Pienaar and Rob Herring added further five-pointers to condemn the visitors to an 11th straight Pro12 defeat.
It was a similarly one-sided affair at the Liberty Stadium where hooker Sam Parry helped himself to a hat-trick of tries as the Ospreys crushed Zebre 59-5.
Steve Tandy's men, who lost five of their six opening games last season, were 24-0 up within 25 minutes as Parry, Lloyd Ashley and Ashley Beck all found the line.
Zebre conceded 99 tries last season and although Tommaso D'Apice did get them on the board on 35 minutes, their defence swiftly crumbled again as Parry touched down either side of the break before replacements Ben John (2) and Dafydd Howells completed the rout.
Leinster were expected to make equally short work of Benetton Treviso at the RDS Arena, but ultimately had to settle for a largely unimpressive 20-8 win.
Although fly-half Joey Carberry scored two tries for last season's beaten finalists, it was not until James Tracey went over seven minutes from time that they made the game safe.
The visitors' points came via a Marco Fuser try and a Tommaso Allan penalty.