The Exiles had to play the final 20 minutes with only 14 men after hooker David Paice was sent off for an off-the-ball incident, but they scored two stunning late tries to seal a win which puts them in control of Pool A.

The hosts made a dream start as wing Alex Lewington crossed the whitewash in just the fourth minute, benefitting from a magnificent off-load out of the back of the hand from full back Andrew Fenby.

Things got even better for Irish five minutes later as they demonstrated their forward power by winning a penalty try, awarded after Grenoble infringed at a trio of scrums in front of their own posts.

However the visitors hit back almost immediately, earning a line-out on the Irish five metre line after the Exiles failed to deal with the restart.

And the Frenchmen set up a rolling maul of their own which hooker Laurent Bouchet finished off by touching down. Captain James Hart knocked over the conversion to leave the score 12-7.

The Exiles ability to hit the self-destruct button was in evidence shortly after, as Lewington attempted a pass which was never on, and Bouchet intercepted for a second try in quick succession.

London Irish then completely fell apart and conceded three quick penalties, one kicked from close-range by Hart, and two monstrous efforts from inside his own half by impressive full back Julien Caminati.

The Exiles stopped the rot as Geraghty slotted a penalty of his own, but a further two three-pointers – the second a fabulous 40-metre drop goal from Caminati – put Grenoble 27-15 to the good.

However Irish landed a blow of their own on the stroke of half-time, as captain George Skivington crashed over at the back of a 12-man rolling maul, albeit that Geraghty missed the conversion.

The hosts continued to build up a head of steam in the second half, scoring two more penalties before Grenoble lost two players to the sin-bin – prop Jono Owen and flanker Mahamadou Diaby.

But they blew a golden opportunity on the Grenoble five-metre line when they conceded a scrum penalty, allowing the visitors to clear their lines.

And disaster struck with little more than 20 minutes remaining, Paice receiving his marching orders for allegedly clearing a ruck in over-enthusiastic fashion.

However the Exiles showed their spirit to go back in front as another powerful drive resulted in substitute Geoff Cross dotting down.

Grenoble – though playing with a largely second-string side – did not fold and looked like they would grab the win when they scored two more tries.

Firstly, the irrepressible Caminati cut a beautiful line to go over just to the right of the posts, before Louis Marrou was the beneficiary of another rolling maul. With just five minutes remaining, Irish trailed 31-41 and it appeared their season was finished.

But Glenn Delaney's men rallied themselves and after hammering away at the Grenoble line, replacement scrum half Tomas O'Leary threw a huge mis-pass which Fenby collected, the full back diving over to make it 41-36.

And quite remarkably, just two minutes later Irish were in front. An overthrown line-out went all the way into midfield, where replacement fly-half Myles Dorrian swooped on it and burst through to score under the posts. Tom Homer kicked the conversion and the Exiles now simply had to hold on.

And that they did, showing remarkable composure to secure the restart and win a scrum before O'Leary kicked the ball in to touch to seal the most astonishing of wins.

London Irish: Fenby; Ojo, Mulchrone, Sheridan, Lewington; Geraghty, Steele; Court, Paice, Aulika; Skivington (capt), Sinclair; Guest, Cowan, Treviranus.

Replacements: Stevens, Halavatau, Cross, Leo, Low, O'Leary, Dorrian, Homer.

Grenoble: Caminati; Caire, Mignot, Messina, Kilioni; Michallet, Hart (capt); Dardet, Bouchet, Owen; Hand, Skeate, Marrou, Diaby, Faure.

Replacements: Jammes, Coulson, Edwards, Goze, Rey, Henry, Saseras, Gelin.