The Exiles came storming out of the tunnel, and raced into a 10-0 lead within seven minutes; first fly-half Barry Everitt landed an early penalty, and then centre Geoff Appleford crossed the line for a try which Everitt converted.
But Gloucester soon steadied the ship, and some good grafting from the pack saw hooker Olivier Azam over after a quarter of an hour.
Everitt landed another goal for a 13-5 lead, but Gloucester flanker Jake Boer stole a line-out ball and crashed over for Gloucester's second try a couple of minutes later, and Henry Paul clipped over the conversion to bring the Cherry and Whites to within a point.
The second half began as the first had left off, with Gloucester slowly turning the screw and Irish finding no way through, but spirited defence kept Gloucester away from the try-line – Paul's two penalties the only reward for Gloucester's work.
When Exiles replacement Mark Mapletoft landed a penalty seven minutes from the end to make the score 18-16, it looked as though the Irish might fight back for an upset – but finally the pressure told, and Gloucester flanker Andy Hazell touched down in the final couple of minutes for the clinching score.
For Gloucester:Tries: Azam, Boer, HazellCons: Paul Pens: Paul 2
For London Irish:Tries: ApplefordCons: EverittPens: Everitt 2, Mapletoft