London Irish (11) 20
Tries: Danaher Pens: Hewat 5
Perpignan (9) 9
Pens: Montgomery 3
Irish scored the only try of the game through Declan Danaher
London Irish reached their first ever Heineken Cup semi-final with an ultimately comfortable win against French side Perpignan.
The visitors went ahead through a Percy Montgomery kick but two Peter Hewat penalties put Irish into a 6-3 lead.
Montgomery levelled it at 6-6 but Declan Danaher soon scored a fine try to put Irish five points clear.
Montgomery cut the gap with his third penalty but Hewat added three more of his own after the break.
The match was billed as a clash of styles between the hosts' pace and adventure and the visitors' more conservative power-based game, and so it proved.
Perpignan had the edge in the scrum but were unable to cope with the Exiles' energy round the park.
Irish also dominated the line-out and second row Nick Kennedy did his England chances no harm with some superb steals on the Perpignan throw.
From the first moment they touched the ball the Exiles played with width and adventure, using long passes in midfield to whip the ball wide to their threatening wingers.
It was a high-risk strategy and when one searching pass failed to go to hand just inside their own half, it gave their Catalan visitors from the south west of France the chance to counter attack.
The hosts managed to get back to haul down Perpignan's powerhouse Romania flanker Ovidiu Tonita but infringed in the process and Montgomery, who kicked South Africa to victory in the World Cup final, stepped up to open the scoring.
The hosts continued trying to play a high-tempo game, with Sailosi Tagicakibau prominent, but a combination of physical defence from the visitors and Irish errors meant they were scoreless after 20 minutes.
They finally got on the board when 6ft 7in second row Kennedy demonstrated the line-out excellence which he is becoming increasingly renowned for.
The England prospect stole a Perpignan throw and when Seilala Mapusua bashed it up the middle former Leicester number eight Henry Tuilagi was penalised at the ensuing ruck and Hewat opened the hosts' account with a penalty.
A couple of minutes later Perpignan's Scotland scrum-half Chris Cusiter dithered after fielding a Mike Catt kick and Hewat was once again on target from distance to put the hosts 6-3 ahead.
Exiles fly-half Mike Catt was forced off by injury late in the first half
Montgomery soon levelled the scores with his second penalty but the hosts hit back with a cracking try.
Kennedy once again stole a Perpignan throw, Mapusua hammered down the far touchline and when the ball was recycled Catt's cross-kick to the corner was picked off by Danaher, who dotted down.
Hewat missed the conversion from wide out and the hosts suffered a blow as Catt, who had picked up a knock a few minutes before, was forced off, with Shane Geraghty coming on to fill the fly-half berth.
A superb corner-flagging tackle by England scrum-half Paul Hodgson denied Adrien Plante a try but Montgomery landed his third penalty to make it 11-9 at the break.
The predicted rain had arrived towards the end of the first half and the giant Perpignan pack began to put the home eight under pressure in the tight in the early stages of the second period.
But Irish played the territorial game superbly through the boots of man-of-the-match Hewat and Topsy Ojo, and two Hewat penalties gave them an eight-point lead after 56 minutes.
In a tight encounter it looked like being a decisive lead and so it proved.
Despite having to chase the game Perpignan looked ponderous when in possession and it was the hosts who saw most of the ball, with former Australia A representative Hewat adding a third penalty with just over 10 minutes remaining.
The match ended in dramatic fashion as Perpignan blind-side Viliami Vaki was red carded for punching as the Exiles booked their maiden Heineken Cup semi-final with some comfort.
They will enjoy 'home' advantage at Twickenham on the weekend of 26/27 April, meeting the winner of Sunday's quarter-final between Toulouse and Cardiff Blues.
London Irish: Hewat, Ojo, Tiesi, Mapusua, Tagicakibau, Catt, Hodgson, Dermody, Paice, Rautembach, Kennedy, Casey, Danaher, S. Armitage, P. Murphy.
Replacements: Lea'aetoa, Coetzee, Hudson, Thorpe, D. Armitage, Richards, Geraghty.
Perpignan: Montgomery, Manas, Marty, Grandclaude, Plante, N. Laharrague, Cusiter, Chobet, Tincu, Mas, Alvarez, Hines, Vaki, Tonita, Tuilagi.
Replacements: Guirado, Freshwater, Bozzi, Porcu, Durand, Hume, Chouly.
Referee: Alain Rolland (Ireland)