Catt gets the cream as Irish clear path to Twickenham

One of these sides knew they would finish their season back where it had started, at Twickenham, and after a gripping and fractious Guinness Premiership play-off it was London Irish who earned a debut final next Saturday. The Exiles could have had a hatful of tries were it not for desperate Harlequins defence, but two were more than enough.

In the London Double-Header last September, Harlequins and Irish won against Saracens and Wasps, and that form held good in the subsequent eight-month slog. Supporters at this meeting of second v third mingled before kick-off; the lady with the Guinness cans sewn into her hat joshing with the fellow in the daft multi-coloured slacks. Still, there was a tension on the field commensurate with a semi-final in a madcap and scoreless first half of one yellow card, six missed penalty goals out of six attempts and a couple of massed brawls.

Irish scrummaged to a ruthless blueprint of boring in on Quins' tighthead, Mike Ross, on every home put-in. Wheeled scrums were commonplace and Ross must be looking sideways at his cornflakes this morning. The referee, Chris White, penalised Irish for it once or twice but the overall effect was to make Quins nervous on their own ball. They were shoved off it near their line after 22 minutes, leaving the ball at the feet of Mike Catt at No 8 (it's a London Irish thing), but his wing, Sailosi Tagicakibau, was held up.

And that was the way of it before the interval: chances made, chances missed. Nick Evans, Quins' All Black fly-half, played with his right knee – his kicking leg, to boot – strapped heavily and he hooked two awfully tentative shots wide from 25 and 30 metres out in the opening nine minutes. The flow was punctuated by stoppages for a punch-up sparked by Catt's high tackle on Danny Care and treatment to Ugo Monye, who was able to resume after being tipped up and over through a cartwheel by Adam Thompstone. Nick Kennedy, Irish's England lock, came off with an injured knee and was replaced by James Hudson.

Mike Brown took over the kicking tee – it had to be done, as Evans was so clearly struggling – but was off- target from slightly longer range than his No 10 after 10 and 40 minutes. Irish's followers might have laughed themselves silly had Peter Hewat, their team's full-back, not put two horrible kicks wide from just outside the 22 in between Brown's efforts. When Tagicakibau went to the sin-bin for a trip on Care a minute before half-time, the lady with the Guinness cans must have been looking for a top-up

But always Irish had their noses in front, like a game stayer at the Cheltenham Festival. Common sense said Evans's overall generalship must have been compromised; though by how much was difficult to judge as he punted capably and began the second half with a rapid break which was only cut down by Delon Armitage's smart tackle. It was Armitage who finally put points on the board, with a penalty lashed over after 42 minutes – see, lads, it was that easy – and in the 52nd minute Irish, the only winners at the Stoop in the regular Premiership programme, had a invaluable try. From a ruck on the left Catt's lovely flat pass found Hudson gallumphing past a badly fractured home defensive line. Catt, Irish's fly-half (and backs coach) when he is not packing down in scrums, may be 37 but the old skills glimmered lustrously.

Armitage converted for 10-0, and as the fourth quarter arrived, Quins sent on Andy Gomarsall and Waisea Luveniyali for Care and Evans. The scrum-half shook his head; Evans could have no complaint. Quins' season, their third back in the Premiership after one spent down in National League One, was sliding away and although the No 8 Nick Easter enjoyed a couple of charges down Catt's channel, there was too little input from his normally influential flankers, Chris Robshaw and Will Skinner.

Irish had been a gnat's whisker away from other tries, through Steffon Armitage and Tagicakibau in the first half and Delon Armitage and the replacement hooker, James Buckland, in the second. After Gomarsall forced a pass and Catt ran in an interception try after 74 minutes, Armitage's conversion kept Irish in good company with Ireland, the Six Nations champions, Munster, the Magners League winners and Leinster, finalists in the Heineken Cup. And that's no blarney.

Harlequins: M Brown; T Williams (DW Barry, 68), G Tiesi, J Turner-Hall, U Monye; N Evans (W Luveniyali, 61), D Care (A Gomarsall, 61); C Jones, T Fuga (G Botha, 53), M Ross (M Lambert, 70), J Percival (J Evans, 54), G Robson, C Robshaw (T Guest, 62), N Easter, W Skinner (capt).

London Irish: P Hewat; A Thompstone (T Homer, 61), D Armitage, S Mapusua (E Seveali'i, 70) S Tagicakibau; M Catt (P Richards, 76), P Hodgson; C Dermody, D Coetzee (J Buckland, 61), R Skuse (A Corbisiero, 49), N Kennedy (J Hudson, 26), B Casey (capt), D Danaher, C Hala'ufia (R Thorpe, 49), S Armitage.

Referee: C White (Gloucestershire).