Edinburgh capitalised on the late change of venue for the second leg of the 1872 Cup to beat Glasgow Warriors 14-11 and retain their hold on the Scottish title.
Munster halted their five-game losing run and completed the double over Ulster this season by beating their interprovincial rivals 9-7 on Saturday to stay in touch with the leading sides in the Guinness PRO12.
Ospreys saw off a second-half comeback from Newport Gwent Dragons to clinch a hard-fought 12-7 Guinness PRO12 win and make it two Welsh derby victories out of two in the space of six days.
Munster fell to their fifth straight defeat in all competitions as Zane Kirchner's last-minute intercept try sealed a 24-7 win for Leinster at Thomond Park.
Full-back Rhys Patchell landed a dramatic last-gasp penalty to secure a derby day victory for Cardiff Blues over Newport Gwent Dragons at Rodney Parade.
Edinburgh sent Glasgow packing empty-handed from the capital for the second season running as the Gunners took a step towards reclaiming the 1872 Cup with a 23-11 first-leg win.
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.
The Ospreys claimed their 12th win in 15 games over the Scarlets, winning an entertaining Guinness PRO12 derby 27-26 in Llanelli – re-vitalising their play-off hopes.
Glasgow Warriors head coach Gregor Townsend has ended speculation about his future after penning a two-year contract extension with the Scotstoun side.