Zebre put on a spirited showing but ultimately fell short against Pro14 heavyweights Leinster.
Leicester Tigers limped to defeat at Saracens, meaning the victors once again sit top of the Premiership.
New Zealand Conference giants the Crusaders and the Hurricanes each came through testing openers in Super Rugby on Saturday.
Leaders Exeter Chiefs suffered a third Premiership defeat of the season at Gloucester, while Wasps moved into the top four.
Centre Stuart McCloskey celebrated a century of matches for Ulster by dotting down for the only try against the Ospreys.
Sio Tomkinson's red card made a Highlanders comeback look unlikely, but Aaron Smith had other ideas and punished the Chiefs.
England thrashed France 44-8 in the Six Nations, with wing Jonny May scoring three of his side's six tries at Twickenham.
It was another struggle for Wales but Warren Gatland's side battled their way to a 26-15 Six Nations win over Italy in Rome on...
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Conor Murray, Jacob Stockdale and Keith Earls crossed for tries as Ireland got up and running in the Six Nations at Murrayfield.
Henry Slade scored two of four England tries as they consigned Ireland to a first home defeat since November 2016.
The Cheetahs stretched their winning run to four Pro14 games after withstanding a Southern Kings fightback in a pulsating derby clash.
Scotland were comfortable winners over Italy in their Six Nations opener, with Blair Kinghorn registering his first international hat-trick.
France led 16-0 at half-time in the driving rain in Paris, but they fell apart in the second half to start the Six Nations...
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Toulouse replaced Clermont Auvergne at the summit of the Top 14 table on Sunday, while Toulon scored two late tries to stun Stade Francais.
Clermont had not been beaten since October, but they were brought back down to earth by Top 14 champions Castres.
Southern Kings produced a stunning late fightback to claim only their second win of the season, halting Edinburgh's impressive run.