Rory Best scored two tries but Ulster's bid to overtake Edinburgh came to an end with a 24-24 draw away to Munster.
Johan Goosen's return to rugby was spoiled by Munster, who engineered an impressive second-half turnaround at the Cheetahs in Pro14.
Edinburgh were beaten at home by Ulster in the Pro14, while the Ospreys thumped Connacht in Swansea.
The semi-final line-up in the European Challenge Cup is complete, after Gloucester and Cardiff Blues reached the last four on Saturday.
There were wins for Glasgow Warriors, Edinburgh and Cheetahs in Pro14 on Saturday, with Duncan Weir among the star performers.
Connacht looked set for a valuable win in Bloemfontein but Niel Marais had other ideas, getting Cheetahs their first victory since January.
Leinster's big win on Saturday did not quell Scarlets as they kept pace in the Pro14, while Benetton Treviso's promising form was ended.