Bob Casey enjoyed a happy homecoming as he helped London Irish edge out defending champions and former employers Leinster 12-9 in a bruising Heineken Cup encounter at the RDS.
Replacement Ryan Lamb emerged as the unlikely hero, putting his kicking demons behind him to boot two crucial second-half penalties for Irish, with the match-winning kick coming in the 80th minute.
Leinster will feel aggrieved as this was a match they could and should have won. They were the side that came closest to breaking the try deadlock, but they never built on a strong opening quarter.
Jonathan Sexton's third successful penalty of this defence-dominated clash levelled it with five minutes to go, only for Lamb to brilliantly steal the headlines with a thumping kick from just inside the hosts' half.
After losing their Under-20s Six Nations crown to England Under-20s in a thrilling final round, France Under-20s lock Tristan Labouteley insists his side will be out for revenge at this year's Junior World Championship.