Robbie Henshaw handed Ireland an RBS 6 Nations fitness boost as Connacht thrashed Enisei-STM 47-5 to qualify for the European Challenge Cup quarter-finals.
A late penalty from Steven Shingler clinched a hard-fought 21-19 victory over Connacht at Parc y Scarlets to send the hosts back to the top of the Guinness Pro12.
Nick Williams' 76th-minute try proved to be the deciding score as Ulster ended Connacht's unbeaten home record this season, winning a closely-fought Guinness PRO12 derby 10-3 at the Sportsground.
Newcastle Falcons put themselves back in contention for the European Challenge Cup’s quarter-finals with a bonus point victory over Connacht on Sunday.
Cardiff staged a stunning comeback to claim a 37-27 bonus-point win over Montpellier to keep hopes of qualifying for the European Challenge Cup's knockout stages alive.
European Rugby Challenge Cup champions Gloucester began their defence with a 23-10 win over Zebre while elsewhere London Irish beat Agen, Cardiff Blues thrashed Calvisano, Worcester beat La Rochelle and Connacht beat Enisei-STM.
Two tries from Darren Dawidiuk and Jonny May in the last five minutes of extra time gave Gloucester a 40-32 win over Connacht and a place in next week's Champions Cup play-off final.
There were wins for Cardiff Blues, Exeter Chiefs, Gloucester and Stade Francais as the second round of European Rugby Challenge Cup fixtures drew to a close today.
Leinster's greater strength in depth helped them complete a festive derby double at the Sportsground as they got the better of a youthful Connacht side with a 16-8 triumph.
After this weekend there is a strong 14 points that separates Leinster at the top of the leader board from Welsh side Ospreys who narrowly beat Edinburgh this weekend.
During a busy Six Nations, the Celtic and Italian sides are in action this weekend, with squads being stretched due to the unavailablity of international stars.