Flutey's penalty snatched victory
London Irish: (8) 20
Pens: Flutey 4
Harlequins: (9) 19
Pens: Jarvis 4
Riki Flutey kicked a last-gasp penalty to condemn Harlequins to defeat on their return to the Premiership.
Quins looked to have sealed victory when Ceri Jones crossed and Adrian Jarvis fired over the conversion just five minutes from time at Twickenham.
But Exiles fly-half Flutey, who had already landed two penalties and a drop-goal, snatched the win.
Quins led 12-8 at half-time thanks to four penalties from Jarvis, with Topsy Ojo scoring a try for Irish.
London Irish director of rugby Brian Smith
"Riki (Flutey) has worked very hard with Dave Alred in the pre-season and he has come of age as a kicker.
"We are disappointed we had to resort to kicking penalties to win the game. Ideally we would like four tries every time.
"We are not entirely happy with the performance but we will take the result."
Harlequins director of rugby Dean Richards
"The boys were bitterly disappointed to lose this one.
"It wasn't the fact we lost in the final two minutes, it was that we didn't execute things the way we wanted.
"We didn't mix our game up very well. Our performance wasn't up to the standard that they expect from themselves."
London Irish: Armitage, Ojo, Feaunati, Catt, Tagicakibau, Flutey, Hodgson, Lea'aetoa, Coetzee, Skuse, Kennedy, Casey, Roche, Magne, Leguizamon.
Replacements: Hatley, Russell, Fitter, Murphy, Danaher, Horak, Everitt.
Harlequins: Brown, Harder, Luscombe, Abbott, Monye, Jarvis, So'oialo, Jones, Hayter, Nebbitt, Spanghero, Miall, Vos, Volley, Easter.
Replacements: Ross, Richards, Evans, Skinner, Keogh, Mehrtens, Duffy.
Referee: David Rose (RFU)