The match – which also marked the opening of the new-look head-quarters of Connacht – saw former Ireland Under-21 coach Michael Bradley take the Connacht coaching reins after succeeding South African Steph Nel.
Two early penalties from Connacht's Ireland 'A' fullback Mark McHugh cancelled out an Ed Thrower try for the Exiles.
But Kevin Barrett nudged the visitors ahead with their second try, converted by Irishman Barry Everitt after 20 minutes for a 12-6 advantage.
Connacht – after some good moves previously – finally crossed the whitewash when wing Darren Yapp scored their opening try on the half hour, converted by McHugh.
Exiles wing Paul Sackey however crossed just before the interval, although Michael Swift squeezed one in just ahead of the whistle being blown for the hosts.
The second half was a more defensive affair, seeing both sides get a good run-out before their respective seasons kick off in the coming weeks.
London Irish face a trip to Belfast where they meet Ulster on Friday, while Connacht host Celtic League champions Munster in Galway on the same evening.
The scorers:
For Connacht:Tries: Yapp, SwiftCon: McHughPens: McHugh 2
For London Irish:Tries: Thrower, Barrett, Sackey.Cons: Everitt 2
