Connacht beat Munster at Thomond Park for only the second time since 1986, while Leinster worked hard to see off Ulster at the RDS Arena.
Munster 20-24 Connacht
Conor Fitzgerald came back to haunt his home province as his 14-point haul helped Connacht beat Munster 24-20 and claim only their second win at Thomond Park since 1986.
Connacht ran in three tries to Munster's two in this bruising derby, but a hat-trick of interprovincial victories eluded Johann Van Graan's men, the Guinness PRO14 Rainbow Cup leaders.
Former Munster prospect Fitzgerald piled up a dozen points, including a crisply-taken 26th-minute try, to steer Connacht into a 17-14 half-time lead.
Munster had replied with forwards-inspired tries from James Cronin and Rhys Marshall, although a restart blunder allowed Sam Arnold over for the visitors' second score.
Still, the table-toppers made sure Shane Daly's sin-binning was not too significant, and they negated Kieran Marmion's try with penalties from Ben Healy and replacement Joey Carbery.
Andy Friend's men, who leaked 50 points to Leinster last Saturday, stood firm, though, with an inspiring defensive performance to match their last success in Limerick in 2015.
Leinster 21-17 Ulster
Tries from British and Irish Lions duo Jack Conan and Robbie Henshaw did the damage for Leinster in a hard-earned 21-17 win over Ulster at the RDS Arena.
Following Munster's defeat to Connacht, Leinster are now right back in the hunt for a place in next month's north-versus-south Guinness PRO14 Rainbow Cup final.
An intense first half finished at seven points apiece, Cian Healy cancelling out Robert Baloucoune's opening try with both defences thoroughly tested throughout.
Following a Billy Burns penalty, the hosts kicked it up a gear with replacement Conan and player of the match Henshaw both crossing before Craig Gilroy's late score.