An impressive first-half onslaught by Celtic League champions the Ospreys at the Sportsground paved the way for their first ever win over Connacht.
Connacht (8) 13
Tries: Lacey, Mostyn
Ospreys (22) 22
Tries: Thomas, Henson, Williams
Cons: Henson (2)
Tries by Jon Thomas, Gavin Henson and Shane Williams gave a comfortable lead.
Matt Lacey got a try when sin-binnings had reduced the visitors to 13 men and Matt Mostyn claimed a late score, but a comeback was never threatened.
The defeat, in Eric Elwood's last game at the ground, leaves Connacht struggling to get a Celtic Cup place.
The result also boosts Cardiff Blues' chances of overtaking the Irish side for a possible Celtic Cup spot and a Heineken Cup play-off place.
Connacht, playing with the wind, opened the scoring with a Mark McHugh penalty, but the Ospreys soon began to put the phases together and stretch the home team.
Full-back Henson levelled it with a penalty following a strong scrummage, then after another fluid attack a neat Matthew Jones inside pass saw lock Thomas power over for the opening try.
Fly-half Jones was involved in the second try from another swift attack, his pass freeing Henson who glided in from 20m, beating opposite-number Mostyn with a nonchalant side-step.
The score took Henson past the 500 point mark in Celtic League rugby.
The Ospreys' powerful scrum platform was the basis for the next score, the ball coming to the backs where excellent interplay between Henson and David Bishop sent Shane Williams on a clear run to the line.
Connacht came back with a series of driving line-outs near the visitors' line, and with the defence getting increasingly desperate James Bater and Duncan Jones were sin-binned.
A penalty try looked inevitable until flanker Matt Lacey emerged with a score from another strong forward drive against the Ospreys' 13 men.
Hopes of an Irish comeback were hit before the break, though, as Stephen Knoop was yellow carded.
The Ospreys saw out the rest of their players' sin-bin time as Connacht's attempts to get back into the game were thwarted by handling errors and the champions' solid defence.
A dismal second half looked set to end scoreless until Mostyn was able to force his way over for an injury-time try.
A conversion would have given the Irish a bonus point for finishing within seven, but McHugh pulled his kick wide, a miss that could prove costly in the end-of-season shake-down.
Connacht: Mostyn, McPhillips, Yapp, McHugh, Slemen, Elwood, Keane, Hogan, Fogerty, Knoop, Short, Farley, Swift, Lacey, J. O'Sullivan.
Replacements: Downey for Slemen (53), Warwick for Elwood (53), Walls for Keane (69), Jackman for Fogerty (53). Not Used: Clarke, Carroll, O'Connor.
Ospreys: Henson, Terblanche, D. Bishop, Parker, S. Williams, M. Jones, Spice, D. Jones, B. Williams, A. Jones, Newman, Thomas, R. Jones, Pugh, Bater.
Replacements: Mustoe for M. Jones (72), James for D. Jones (79), R. Hibbard for B. Williams (79), Millward for A. Jones (56), Bateman for Newman (69), Tandy for Pugh (79). Not Used: A. Bishop.
Referee: Ian Heard (Scotland)