Racing 92 secured a hard-fought 34-30 win over Munster, while there were also European Champions Cup victories for Leinster, Toulon and Castres on Sunday.
Despite the loss, Munster remain at the summit of Pool 2 as they earned a losing bonus point against Racing, who sit a point below them in second.
Racing struck early with a try from Yannick Nyanga but Munster were kept in the contest by a Jean Kleyn try, which made it 13-7 at half-time.
Marc Andreu scored early in the second half for the Parisians, but Munster then took the lead through tries from Keith Earls and Chris Farrell.
Racing regained the lead through Dimitri Szarzewski and the boot of Maxime Machenaud to grind out a win.
In other results on Sunday, Leinster secured a home quarter-final with a dominant 55-19 win against the Glasgow Warriors. Montpellier and Exeter will compete for second place in Pool 3.
Toulon produced an equally strong showing as they overcame a determined Treviso side 36-0. Toulon’s match against the Scarlets will now decide which team finishes on top of Pool 5. Should Toulon lose the match and Bath get a bonus-point win against Treviso, Toulon will not qualify for the playoffs.
Castres produced a strong first-half performance to beat the Leicester Tigers 39-0. The defeat confirmed the Tigers’ exit from the competition as they sit bottom of Pool 4 with one win from five matches. Castres are third in the pool and need four points from their next match against Munster to stand a chance of qualifying for the playoffs.
Champions Cup results (Round 5):
Northampton Saints 34 Clermont 21
Ospreys 15 Saracens 15
Ulster 20 La Rochelle 13
Harlequins 33 Wasps 28
Exeter Chiefs 41 Montpellier 10
Bath 17 Scarlets 35
Racing 34 Munster 30
Leinster 55 Glasgow Warriors 19
Toulon 36 Treviso 0
Castres 39 Leicester Tigers 0
Photo: Dan Sheridan/INPHO