Bath welcomed back England trio Steve Borthwick, Matt Stevens and Lee Mears and Wales international Gareth Delve but two blunders in first-half injury time gifted Irish two tries and a 26-6 half-time lead.
Irish dominated the opening minutes and, after two lineouts and two scrums near the Bath line, No8 Juan Leguizamon picked up from the back of the scrum to score.
Bath fly-half Chris Malone landed a 24th-minute penalty but Irish responded with a superb try from England international Topsy Ojo. A quickly taken Delon Armitage lineout caught Bath unprepared and Ojo sidestepped his way through Bath’s defence before charging 30 metres to score.
Malone added another penalty to make it 12-6 but two howling errors gifted Irish two tries in injury time.
The first was when Bath prop Duncan Bell carelessly lost possession and Armitage pounced on the ball.
The second try came when Bell’s pass was intercepted by Ojo. Both scores were converted by fly-half Riki Flutey.
Bath recovered their composure and a minute into the second half a well executed Bath’s lineout set up No8 Delve. Five minutes later and a Bath lineout catch and drive sent hooker Mears over on the right wing. With Malone adding a conversion a and a penalty Bath trailed just 21-26.
The Exiles responded with a 76th-minute Sailosi Tagicakibau try for a 33-21 lead.
Bath who had the final word with another successful lineout catch and drive manoeuvre which set up centre Alex Crockett when the ball was switched out wide.
Crockett’s injury time score was not enough to steal the win but enough to at least salvage an important losing bonus point for struggling Bath.