London Irish captain Bob Casey described his team's shock win at Leinster as a "special moment" after levelling the defending Heineken Cup champions in Dublin
Ryan Lamb kicked two crucial second-half penalties, including the 79th-minute winner, as the Exiles stunned the holders 12-9 at the Royal Dublin Showground.
Peter Hewat also kicked two penalties in a tight contest while Jonathan Sexton converted three kicks, including a late effort that looked to have salvaged a draw for Leinster.
However Lamb struck late before the London Irish defence produced a remarkable rearguard action to hold Leinster out.
Casey said: "This is a special moment for the club and it just shows how far we have come.
"We always knew we would get stronger as the game went on. We have worked hard on our fitness and conditioning and we knew we would still be in their in the final 15 minutes.
"It was a little ropey towards the end and I thought we may have blown it when we gave away the late penalty at the end. But the determination and spirit in this squad is incredible and we just kept going.
"We put their lineout under huge pressure, the scrum came good and our back-row was outstanding at the breakdown.
"However we have not won anything yet. We have the Scarlets next Saturday and this win will mean nothing if we don't follow it up by winning at home."
The man of the match award was extra special for Dubliner Casey on his return to his home-town.
He added: "That does make it even more special. I had a lot of family in the crowd and I was pleased to come back and give them something to celebrate."