A mammoth late penalty from Scott Spedding snatched a 24-21 win for Clermont Auvergne to extend Saracens' losing streak to seven matches, and Elliot Daly starred as Wasps ended La Rochelle's 100 per cent European Champions Cup record.
Injury-hit Sarries were subjected to a 46-14 mauling by the Top 14 champions in a Pool 2 clash rearranged for Monday due to snow, but looked much more like the side that has won back-to-back Champions Cup titles at a raucous Stade Marcel-Michelin on Sunday.
A superb early Ben Spencer solo try and eight points from the boot of Owen Farrell gave fired-up Sarries a 13-0 lead inside 10 minutes, but three Morgan Parra penalties and one from Spedding reduced the deficit to just a point at half-time.
Another two successful Parra kicks from the tee made it advantage Clermont, who lost wing Alivereti Raka - scorer of a quickfire hat-trick at Allianz Park six days earlier - and France centre Damian Penaud to injury in the first half.
There were howls of derision from the Clermont faithful when Nick Abendanon was shown a yellow card for taking a man out in the air after another penalty from Farrell, who then fed Alex Lozowski to put Sarries 21-18 to the good 17 minutes from time.
Farrell failed to convert as whistles reverberated around the stadium and Parra levelled a classic contest with Juan Figallo in the bin, Spedding providing the final twist by stepping up to hold his nerve under pressure to put Clermont seven points clear of Sarries.
Ospreys moved above the holders into second spot with a 32-15 bonus-point win in Northampton Saints' first match since director of rugby Jim Mallinder's sacking, Rhys Webb claiming a double at the Liberty Stadium.
Top 14 leaders La Rochelle remain top of Pool 1, but Wasps breathed new life into their bid to qualify for the quarter-finals with a 21-3 success at the Ricoh Arena inspired by Daly.
The versatile England international scored a try in each half before limping off and Tom Cruse also barged his way over in a richly deserved victory which put Wasps five points behind their opponents, who hammered the Premiership side 49-29 last weekend.
Ian Keatley booted 20 points and CJ Stander scored a second-half try to give Munster a 25-16 win to go four points clear at the top of a tight Pool 4, their first success at Leicester Tigers in 11 years spoiling Manu Tuilagi's comeback and leaving the Premiership side facing elimination.