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Leinster recorded a victory away to the Cardiff Blues in the Pro12, before Connacht won a high-scoring encounter at Zebre.
Leinster’s 14-13 success brought Leo Cullen’s side to the top of the table but Connacht quickly took over first place with their 51-34 triumph in Italy.
In Wales, Leinster welcomed back six of the Ireland squad that lost out in France last weekend, along with Cian Healy from injury.
The visitors, with a strong wind to their advantage, bossed the first half but only led 6-3 at the interval, following a mediocre penalty battle between Gareth Anscombe and Ian Madigan.
The number tens' kicking fight continued to dominate affairs until Jack Conan came off the blindside of a maul and fed Isa Nacewa, who finished with ease.
Madigan missed the conversion attempt, leaving Leinster 14-6 ahead with a quarter of the encounter remaining.
Following a yellow card for the away side's Jordi Murphy, Cardiff pushed hard at their opponents late on, with Josh Navidi driving over to score from a line-out.
Rhys Patchell added the extras to bring the hosts to within a point but the full-back was unable to land a late drop-goal attempt, confirming Leinster's triumph.
Worse still for Cardiff - and Wales - was that Cory Allen suffered what appeared to be a serious ankle injury that may well keep the centre out of the remainder of the Six Nations campaign.
At the Stadio Sergio Lanfranchi, Tries from Matt Healy and Kieran Marmion helped Connacht to a 17-13 half-time lead over Zebre, with Johan Meyer having hit back for the hosts just prior to the interval.
During a hectic beginning to the second period, Healy's second and third tries of the day, either side of a score from the hosts' Kelly Haimona, left the Irish side 31-20 ahead with a half-hour remaining.
Dries van Schalkwyk's try gave Zebre hope but a brace from Niyi Adeolokun eased the visitors' nerves.
An effort from Federico Ruzza proved to be merely a consolation for the Italian outfit.
Craig Ronaldson kicked nine points for Connacht, with Alan MacGinty adding 12 of his own.
Pat Lam's troops top the Pro12 table, three points ahead of Leinster, but the Westerners have played a game more than the Dublin-based men.
Ulster will bring about a third change of the weekend at the summit of the ladder, should they record a bonus-point triumph over the Scarlets in Belfast on Sunday.