LONDON - Clermont's hopes of becoming the first team to guarantee a European Champions Cup quarter-final spot stalled in a 34-21 loss at Northampton on Saturday.
The injury-ravaged French side, who had won all four of their Pool 2 games this season, also failed to garner a losing bonus point and could be overtaken as group leaders by Ospreys who face defending champions Saracens later Saturday.
Northampton, who have no chance of qualifying for the last eight, ran in five tries courtesy of Teimana Harrison, Nafi Tuitavake, Ben Foden, Ken Pisi and Cobus Reinach.
Clermont, the runners-up last season, may now need to beat Ospreys at home next weekend in a potential pool decider.
Adding to the French team's woes was an injury suffered by international lock forward Arthur Iturria who had only been on the field for 12 minutes at Franklin's Gardens when he limped off with a right leg problem.
Clermont have been ravaged by injuries this season, so much so that last weekend they were forced to field nine youth players in their matchday squad in the 58-6 rout by Racing 92 in the Top 14.
"The season is very complicated for us at the moment," said Clermont's English winger Nick Abendanon.
"We have virtually an entire team in the casualty room but we remain a great side. We will just have to finish the job at home next week."
On a miserable day for French clubs, Ulster moved top of Pool 1 with an impressive 20-13 home victory over La Rochelle.
Exeter inflicted another setback for French hopes when they crushed visiting Montpellier, 41-10 later in the afternoon.
La Rochelle could have ensured a place in the last eight with a win but will enter the final round of games trailing Ulster, who leapfrogged the French side with the win, by a single point.
The victory represented a rapid change in form by Ulster, thrashed 38-7 away to Leinster in the Pro14 last week.
"Today we knew that we had to do better against a team as good as La Rochelle," try-scorer Rory Best said after the match. "We showed the determination and resilience of our side."
Harlequins later downed Wasps 33-28 to leave the destiny of the pool in the hands of Ulster and La Rochelle.
Wasps' England flanker James Haskell was sent off for a dangerous tackle on Jamie Roberts late in the game and faces a suspension that could affect his availability for the Six Nations.
Dave Ewers scored a 28th-minute try to give Exeter a narrow half-time lead against Montpellier at Sandy Lane.
Montpellier cracked after the break as Exeter scored five tries in 19 minutes, the pick of them two acrobatic touchdowns in the left corner by Olly Woodburn.
Exeter helped themselves, climbing to second in Pool 3, a point ahead of Montpellier, but they might have helped Leinster, who can now clinch first place when they host Glasgow on Sunday, even more.
In Belfast, La Rochelle took an early lead with a pair of penalties from Alexi Bales but then lost Paul Jordaan to a yellow card for tackling an opponent in the air.
Against 14 men, Ulster scored a try, touched down by hooker Best after a driving maul.
With La Rochelle back to full strength, Ulster scored again as Jacob Stockdale plunged over near the corner flag. John Cooney missed both conversions in the wind but Ulster led 10-6 at the break.
La Rochelle hit back three minutes into the second half with a try by Bales, who converted. Ulster responded two minutes later with a score from No. 8 Nick Timoney. This time Cooney converted and he added a penalty in the 50th minute to finish the scoring.
In the final round next weekend, Ulster travel to Wasps while La Rochelle host Harlequins.