Connacht bounced back from a disappointing loss away to the Scarlets to put a dent in the play-off hopes of the reigning champions at The Sportsground last night.
Connacht thoroughly deserved their victory with a clinical display which saw them finish strongly to wrap up a badly needed win for Eric Elwood's men in an entertaining clash.
A first-half try from flanker Willie Faloon and the accurate boot of Dan Parks were the primary factors in the victory.
Connacht did not risk centre Dave McSharry, who is troubled by a groin injury, given his prospects of winning his first Irish cap against Scotland on Sunday week following the injury to Gordon D'Arcy.
Connacht had the wind behind them in the opening half and built up a 13-7 interval lead, with Parks getting them off the mark with a penalty after six minutes from the right wing.
But Ospreys worked the ball well through the hands with Kahn Fotuali'i busy as ever at scrum-half and Alun Wyn Jones dictating matters up front in his first start since injury before Christmas.
The Ospreys pressure yielded a 13th minute try. They built the phases after winning a line-out on the right and while the Connacht defence held them at bay for several forays, Fotuali'i tapped a close range penalty and dived over.
Matthew Morgan added the points into the tricky wind to make it 7-3 to the champions.
Connacht lost winger Tiernan O'Halloran to injury, paving the way for skipper Gavin Duffy to come on for his 150th appearance, while the early collisions also took out Ospreys left winger Ben John with a rib injury.
Connacht, getting an edge in the scrums, hit back after 17 minutes. Faloon made the initial break before John Muldoon and Michael Swift took it on down the right and when Swift was stopped he had Faloon coming through at pace to take the pass and drive over for his first league try for Connacht.
Parks negotiated the wind with the outside of his right boot to add the conversion and push Connacht 10-7 in front.
He made it 13-7 by the interval with an effort from 30 metres on the half hour, while an incident three minutes earlier when Joe Bearman lifted Faloon in the tackle could yet see the intervention of the citing officer.
Parks extended Connacht's lead six minutes after the restart with a penalty from 25 metres after Eoin Griffin had done well for the home side.
Parks continued to kick good territory for Connacht and kept Ospreys penned back.
The introduction of Jonathan Thomas gave Ospreys a lot of go-forward ball in the final quarter but their handling let them down at crucial stages as Connacht got the tackles in with centres Kyle Tonetti and Eoin Griffin rock solid.
But Morgan reduced the deficit to six points ten minutes from time when he made no mistake with a 30 metre penalty to leave it 16-10.
Connacht, however, responded to the challenge superbly and countered from deep.
A superb tackle by Robbie Henshaw on his opposite number Richard Fussell presented Parks with an opportunity to put two scores between them and the out-half made no mistake into the wind from 25 metres to the left.
Parks, who had earlier been off target with a drop goal from the right, then wrapped up proceedings three minutes from the end when he sliced the posts with another drop from the right.
After that it was only a matter of playing down the clock as Connacht chalked up only their sixth ever win over the five-time champions.
Connacht – R Henshaw; T O'Halloran (G Duffy 15), E Griffin, K Tonetti, D Poolman; D Parks, K Marmion (P O'Donohoe 70); B Wilkinson (R Ah You 62, Wilkinson 73), J Harris-Wright (E Reynecke 59), N White (R Loughney 40); M Swift, M Kearney (A Browne 53); J Muldoon, W Faloon, E McKeon (J O'Connor 66).
Ospreys – R Fussell; T Habberfield, T Isaacs, J Spratt, B John (R Jones 10, R Webb 66); M Morgan, K Fotiali'i; D Jones (M Thomas 74), S Baldwin, C Griffiths (D Arhip 59); A Wyn Jones (J Thomas 66), J King; J Bearman, S Lewis (L Peers 51), M Allen.
Ref – G Vivarini (Italy).