Niall Annett’s 100th appearance party was ruined by his former school team-mate Paddy Jackson as Warriors suffered an agonising defeat on their first visit to the Brentford Community Stadium.
Annett, who ran out through a guard of honour formed by his team-mates before kick-off, marked his landmark appearance by scoring the first of Warriors’ two second half tries.
When Billy Searle converted Justin Clegg’s maiden Premiership try nine minutes from time, it looked like Warriors would be heading home with more than just a losing bonus point.
Instead Jackson booted over a penalty from the halfway line three minutes later to snatch victory for Irish who spent most of the match under the pump.
Warriors had 80 per cent possession and 72 per cent territory and played composed rugby for long periods of the game.
But 18 turnovers proved costly and Irish made the most of their own very limited supply of possession.
Jackson, who played in the same side as Annett at Methodist College in Belfast, opened the scoring when he banged over a long range penalty after three minutes.
Warriors were soon back on level terms when found the target with a penalty but Irish went ahead again from their first attack of the match, a sweeping one from a lineout which was finished by scrum-half Ben Meehan.
Jackson added the extras but it was Warriors who dominated for most of the next 20 minutes with some patient approach, big carries and intelligent tactical kicking which were undone by handling errors.
Richard Palframan, who was promoted to the bench after Nick Schonert withdrew with a stiff neck, found himself pressed into service earlier than expected as Conor Carey went off with a bicep injury after 18 minutes.
Palframan was in the action straight away when he burst through a tackle and was hauled down just short of the line, but he was unable to get the ball away from the tackle and he beat the turf in frustration as it rolled forward.
Irish absorbed the pressure and scored again when they eventually broke from defence. It required a last-ditch tackle from Matt Kvesic to deny Meehan a second try. But Kvesic was sin-binned for not allowing Meehan to regain his footing, Irish kicked the penalty to the corner, worked infield and Steve Mafi burrowed over for the try which Jackson improved.
Either side of that score, Searle was narrowly off target with two penalty attempts which were to gain in significance as the match wore on.
Warriors continued to dominate in the second half to such an extent that Irish only made a couple of visits into the 22 the most threatening when Jackson kicked ahead and Nick David jinked his way out of trouble.
Superb interplay between Ashley Beck and Kvesic eventually opened up the home defence and Annett, who had a busy afternoon in attack and defence, galloped over for a thoroughly deserved score which Searle improved.
Warriors applied further pressure and patience and persistence was rewarded when Clegg muscled his way over from close range and Searle added the conversion to level at 17-17.
But a penalty at the breakdown, a rare lapse of discipline in the second half, was all Jackson needed to snatch the win and break Warriors’ hearts.
Warriors | 15 Nick David, 14 Perry Humphreys, 13 Francois Venter, 12 Ashley Beck (Morris 54), 11 Tom Howe, 10 Billy Searle, 9 Francois Hougaard, 1 Ethan Waller (Thomas 55), 2 Niall Annett (Miller 55), 3 Conor Carey (Palframan 18), 4 Andrew Kitchener (du Preez 50), 5 Justin Clegg, 6 Ted Hill (C) (Dodd 72), 7 Matt Kvesic, 8 Joe Batley.
Replacements | 16 Isaac Miller, 17 Marc Thomas, 18 Richard Palframan, 19 Tom Dodd, 20 Cornell du Preez, 21 Gareth Simpson, 22 Fin Smith, 23 Oli Morris.
3m | Jackson pen 3-0
6m | Searle pen 3-3
9m | Meehan try 8-3
10m | Jackson con 10-3
34m | Mafi try 15-3
35m | Jackson con 17-3
49m | Annett try 17-8
50m | Searle con 17-10
71m | Clegg try 17-15
72m | Searle con 17-17
74m | Jackson pen 20-17