Harlequins (0) 0
London Irish (0) 17
Hudson, Catt Cons:
D Armitage 2 Pens:
Tagicakibau came within a fingertip of opening the scoring for London Irish
London Irish will play in their first Guinness Premiership final after a hugely impressive win at Harlequins.
With Quins missing four penalties and London Irish failing with two, the score was 0-0 at half-time.
But Delon Armitage then edged Irish into the lead and James Hudson raced over for the first try of the game.
Armitage kicked the conversion and Mike Catt added a late interception try to send Irish to Twickenham to play Leicester in the final on 16 May.
The Tigers had earlier reached the final for the fifth year in a row after downing Bath, and they would have had far more big-match experience whichever side won at Harlequins' Twickenham Stoop ground, with neither London Irish nor Quins having ever reached the Premiership final.
After finishing second in the table and securing a home semi-final, Harlequins were hoping to make the short trip to the final next Saturday, but an outstanding display by the Exiles' pack laid the ground for an upset victory.
An abrasive start was marred when Ugo Monye, leaping to try and claim a high ball, somersaulted over London Irish wing Adam Thompstone - who never took his eye off the ball - and crashed head-first to the ground.
It was a sickening moment but after lengthy treatment the England winger, who is South Africa-bound with the Lions, was able to continue.
Quins could have taken an early lead but the fit-again Nick Evans missed two kickable penalties, pulling them to the left of the sticks.
The former All Black had heavy strapping on his knee and, perhaps emboldened by his inability to bisect the posts, the Exiles soon conceded a third penalty when Catt high-tackled Danny Care as he took a quick tap.
With Evans having more strapping applied Mike Brown took over the kicking duties but his radar was equally wonky and once again the ball drifted well wide of the posts.
London Irish were under the cosh at this stage and Thompstone did well to deny Quins a try from a cute kick ahead before freeing Steffon Armitage at the other end as the visitors finally broke their shackles
The pocket-battleship flanker was just bundled into touch in the right corner and when the Exiles attacked down the other flank a minute later his brother Delon fed Sailosi Tagicakibau, only for the Samoa international to drop the ball as he tried to stretch over in a tackle.
Catt's late intervention was the icing on the cake for Irish
The Exiles, who were dominating the scrums despite losing England second row Nick Kennedy to a knee injury, should have broken the deadlock around the half-hour mark but their Australian full-back, Peter Hewat, contrived to miss two straightforward penalties.
The Exiles lost Tagicakibau to the sin-bin for a cynical trip on Care as the England scrum-half took a trademark quick tap penalty but, inevitably, Brown was off-target with the resulting shot at goal.
The deadlock was finally broken three minutes after the restart as Delon Armitage, who had replaced Hewat, made no mistake with a penalty for London Irish and they soon scored the first try of the game.
Quins played themselves into trouble, with Tom Williams tackled by Paul Hodgson as he tried to kick out of defence while on the run.
Irish swept the ball down the line before switching it back into midfield and Newcastle-bound second row Hudson cut a superb line to score under the posts.
Delon Armitage added the extras and with just under half an hour to play, London Irish had one foot in the final.
Harlequins tried to rally and hurled themselves at the Exiles but the visitors held firm and when they went back on the attack they nearly scored a second try, but Delon Armitage was tackled into touch by the flying Monye as he raced for the corner.
The Quins fans cheered the tackle to the rafters but it was the Exiles supporters who were loudest in the final stages.
And as the Fields of Athenry rang round the Stoop the evergreen Catt sauntered over for an interception try to ensure the Exiles will face Leicester in the final next Saturday.
Harlequins coach Dean Richards:
"We had opportunities to get points on the board but didn't take them.
"It might have been a totally different game had we taken those points at the start. That's life.
"I like to think this is just the beginning. We'll learn from today and will be a better side next year."
London Irish coach Toby Booth:
"This has been one of those purple patch days. I thought we were resilient in the first 20 minutes and we showed some true quality.
"They didn't capitalise with their kicks and neither did we. Then the game began to swung in our favour.
"We made life difficult for ourselves but stood tall and matched their physicality."
Brown; T Williams, Tiesi, Turner-Hall, Monye; N Evans, Care; Jones, Fuga, Ross, Percival, Robson, Robshaw, Skinner, Easter.
Barry for T Williams (69), Luveniyali for N Evans (62), Gomarsall for Care (62), Lambert for Robson (71), Guest for Robshaw (63).
Botha, J Evans.
Hewat; Thompstone, D Armitage, Mapusua, Tagicakibau; Catt, Hodgson; Dermody, Coetzee, Skuse, Kennedy, Casey, Danaher, S Armitage, Hala'ufia.
Homer for Thompstone (65), Seveali'i for Mapusua (71), Richards for Catt (76), Buckland for Coetzee (61), Hudson for Kennedy (27).
Chris White (RFU).