Springbok Rugby World Cup winner Duane Vermeulen scored his first Ulster try as the Irish province left Clermont at risk of missing out on the European Champions Cup last 16 with a 34-31 win on Saturday.
Vermeulen, 35, bundled over with half an hour left on his fourth appearance for the Ravenhill outfit after joining from the Blue Bulls in September.
The 1999 champions were already guaranteed a knock-out place before the game but the French side, runners-up on three occasions, are seventh in Pool A and need Montpellier, who welcome Exeter Chiefs on Sunday, and Glasgow Warriors, who host La Rochelle later on Saturday, to slip up.
Jacobus van Tonder, Alivereti Raka and Judicael Cancoriet crossed for Clermont in the final 10 minutes but the late rally was insufficient to claim a first win in Ireland since 2014 and leaves them potentially missing out on top-tier European knock-out rugby for just the second time in a decade.
"There are a lot of questions of 'what if?'," Clermont head coach Jono Gibbes told BT Sport.
"It will be interesting to see Montpellier's response at home to Exeter and if Glasgow have the pedigree to get over a very good La Rochelle team."
Earlier, four-time winners Leinster swatted Bath aside with a 10-try, 64-7 victory at the Rec to book their place in the last 16.
Winger Jimmy O'Brien ran in four tries as the Irish province shredded the defence of the 1998 champions.
Bath were without 20 of their squad through injury or Covid and lost England flanker Sam Underhill after only 15 minutes when his head collided with Robbie Henshaw's hip.
Elsewhere, Northampton Saints' trip to Racing 92 on Sunday became the 12th of the 48 pool games to be impacted by Covid-19 with the Parisians handed victory due to virus cases in the visitors' squad.
Holders Toulouse risk missing out on the knock-out rounds after their fixture with Cardiff, set for earlier on Saturday, was also cancelled with the Welsh region given the five match points.
The record five-time champions criticised the tournament organisers, European Professional Club Rugby (EPCR), and said they would take legal action against the decision.
French Rugby Federation president and World Rugby vice-chairperson Bernard Laporte sympathised with the double winners.
"I understand the anger of the players and the clubs," Laporte tweeted.
"The decisions of EPCR are unsporting and disheartening," he added.
On Sunday, Munster host Wasps and Stade Francais play Connacht with the results potentially impacting on Toulouse's progress to defend their crown.