James Haskell was sent off for a dangerous tackle as Wasps collapsed to a dramatic 33-28 defeat by Harlequins that all but ends their European Champions Cup quest.
Haskell flattened Jamie Roberts with a shoulder-high challenge in the 76th minute that was also late, receiving a straight red card from referee Roman Poite and ending the groggy Wales centre's afternoon.
The England flanker faces a suspension that could affect his availability for the 6 Nations, but his more immediate concern will be Wasps' implosion at Twickenham Stoop.
Leading 21-0 after 30 minutes, they leaked a succession of tries, grabbed the bonus point, before falling apart once again as touch downs from Danny Care, Elia Elia and James Chisholm completed a remarkable fightback by Quins.
Harlequins' interest in Europe was extinguished long ago - they had lost all four previous matches of this season's group phase - but a team weakened by injury and suspension fought to the end and were rewarded.
It was the 80th minute when man of the match Chisholm picked and drove over from close range as shell-shocked Wasps rubbed their eyes in disbelief at having thrown the game away.
Mathematically they can still qualify for the knock-out phase, but they face mission impossible against pool leaders Ulster at the Ricoh Arena next weekend to progress.
An uneventful first quarter came alive in the 17th minute when Wasps attacked from a line-out and were rewarded by crossing several phases later.
Drives from Haskell and Jake Cooper-Woolley sent Quins backwards before quick hands by Willie le Roux and Thomas Young enabled Kyle Eastmond to accelerate over the whitewash.
Wasps struck for a second time three minutes later when Care and the superb James Lang spilt the ball between them, enabling a counter-attack that saw Nizaam Carr run 60 metres to cross.
Both tries had been scored with Quins prop Lewis Boyce in the sin-bin for tackling Ashley Johnson without the ball and it was the Wasps hooker who touched down for the third.
Route one was the path over the line this time, Joe Launchbury catching the line-out ball as the prelude to a drive that ended when Johnson grounded the ball.
Quins took advantage of a broken field to begin their response, Lang punting ahead for Ross Chisholm to win the foot race and score.
The match was now finely poised and when Care set-off from a five-metre scrum, delaying his pass for Lang to skip over, the home side were over for a second.
Quins' fightback was interrupted 14 minutes after half-time and once again a line-out provided the platform for the undoing.
Young carried into the heart of the defence and with gaps appearing out wide Danny Cipriani was able to send Brendan Macken through a gap to seal the bonus point.
Christian Wade performed a try-saving tackle on Tim Visser but the pressure continued to build through a succession of short-range drives that were completed when Care burrowed over.
All the momentum was with Harlequins and with replacement fly-half Marcus Smith orchestrating play brilliantly, they claimed their fourth try that started with Visser's break inside and finished when Smith sent Elia over with a long floated pass.
And Wasps' fate was sealed when James Chisholm drove across the whitewash with seconds to spare.
Northampton secured back-to-back wins in all competitions for the first time since September as they inflicted a first Champions Cup defeat of the season on Clermont Auvergne.
Saints - already out of Europe following four straight reversals - ran in five tries courtesy of Teimana Harrison, Nafi Tuitavake, Ben Foden, Ken Pisi and Cobus Reinach in a 34-21 victory at a buzzing Franklin's Gardens.
The loss for Clermont, last season's runners-up, also means they must wait until next weekend to secure qualification for the knockout stages.
It had been plain sailing for Clermont in this competition to date with four wins from four putting them in pole position to reach the last eight for another year.
But despite an early effort from Remy Grosso and an Isaia Toeava try, plus the boot of France international Morgan Parra, Clermont were still unable to return to winning ways.
The French giants entered this clash against a Saints side - still finding their feet since Jim Mallinder's December sacking - on the back of three straight Top14 defeats.
Restoring pride was the target for the Alan Gaffney's Saints who made three changes from the dramatic victory against Gloucester last weekend.
Tom Stephenson was in for the injured Luther Burrell with Kieran Brookes and Christian Day bolstering the pack.
It was the visitors who came out of the blocks quickest and went ahead inside two minutes. Wing Grosso was the man to touch down as he powered his way over in the corner with Parra mastering the conversion from the touchline.
The Saints soon settled and found a response on 13 minutes with number eight Harrison touching down in the corner following a surging break from lock Api Ratuniyarawa but Harry Mallinder could not land the conversion.
Clermont extended their lead through full-back Toeava's try and a Parra penalty on 31 minutes. But Northampton battled back before the break when Tuitavake sped through unscathed with his first touch of the ball after replacing the injured Ahsee Tuala.
After the interval, the hosts went into overdrive. First Mallinder kicked a penalty in off the post before wing Foden blitzed his way through out wide. This time fly-half Mallinder was spot on with the extra two points.
Parra hoisted Clermont back ahead with two penalties, while Mallinder could not convert a kickable opportunity to restore the hosts' lead.
But the miss did not matter when Pisi scored the bonus-point try and the inconsistent Mallinder drilled the conversion for a six-point advantage with 15 minutes to play.
Replacement Reinach put the seal on things on 73 minutes - powerfully punching over - as Mallinder kicked the conversion to well and truly rub salt in the wounds of Clermont.
It means Gaffney has now won both of his two games in caretaker charge, the veteran coach making an early case to take on the job full-time for next season, should he want it.