Leinster and Munster had contrasting fortunes in their final pre-season friendlies before the start of the RaboDirect PRO12 campaign next weekend.
Leinster took on Northampton at Donnybrook but were beaten 21-13 by the English side, while Munster hosted London Irish and enjoyed a 27-13 victory.
Ronan O'Mahony grabbed a second-half hat-trick to help Munster to victory over Irish in Musgrave Park.
Rob Penney's side trailed 13-3 after 51 minutes but O'Mahony's tries helped secure the win, as JJ Hanrahan also scored a try for the home side in the 71st minute.
Munster prop BJ Botha looks set to miss next week's opener against Edinburgh after picking up a knee injury and was helped from the field.
After the game Penney said: "All the signs are it will be more than one month. We will assess more over next 48 hours."
Marty Moore's try and a Jimmy Gopperth penalty helped Leinster to an 8-5 lead at half time at the south Dublin venue, however USA international Manu Samoa scored a try for the visitors in the 52nd minute, while Steve Myler landed the conversion and a further penalty to extend the visitors' lead.
Sam Oliver kicked two penalties for Northampton before Dan Leavy scored a try for Leinster in the 79th minute but the English side held on for the victory.