Ospreys (13) 22:
Pens: Connor 3, Durston 2.
Connacht (16) 33:
Tries: Munn, Jackman, McCarthy, McPhillips
Cons: Elwood 2.
Cons: Elwood 2, McHugh.
Ospreys 22-33 Connacht
Connacht put last week's home defeat to the Scarlets behind them by handing out a similar fate to another Welsh side, beating the Ospreys 33-22 at St Helen's.
Lyn Jones' men were coming off a heavy loss away to the Blues and the early signs were that the Ospreys were intent on making amends and maintaining their 100% home record.
But Connacht took a stranglehold over the Ospreys' under-strength scrum, while the Welshmen's handling and decision-making slowly unravelled under the pressure.
Both sides looked well matched in the early stages and the game benefited from the players trying to keep ball in hand.
However, the defences had the upper hand and it required a well-judged box kick from Ospreys scrum-half Andy Williams to create the first scoring opportunity.
The chase was good, forcing Connacht wing Ted Robinson to spill the high ball and his team-mates gave away the penalty as the Irish scrambled back.
Shaun Connor made no mistake with the place kick and the Ospreys fly-half grabbed another three points soon after to make it 6-0 after 12 minutes.
It didn't take long for the visitors to respond and a turnover forced by the Connacht forwards paved the way for a slick backs move to send wing Wayne Munn over unopposed.
The prolific Eric Elwood added a simple conversion, then his first penalty of the night after Ospreys flanker Richie Pugh clumsily entered a ruck from the side.
Suddenly trailing 10-6, the Ospreys responded to their wake-up call and laid siege to the Connacht line.
The Irish tackling was brave and strong but still gave away an easy penalty for Connor to slot his third kick.
No sooner had Connacht kicked off than the Ospreys were back attacking the Irish line.
Connacht's scrum dominated the set pieces at St Helen's
A fine interchange of passing between Adrian Durston, Gareth Morris and James Storey set Connor racing down the left wing.
The ball was spun quickly right and if someone pacier than prop Paul Jones had been on the wing, a try would have been a certainty.
But Connacht had given away another penalty and Ospreys skipper Scott Gibbs boldly opted for the attacking line-out, from which hooker Chris Wells forced his way over for a converted try.
The effort wasn't without cost, however, as Wells was forced to limp off with a knee injury to be replaced by 19-year-old Alun Wyn Davies.
Already down to the bare bones in the front row because of injuries and international demands, the Ospreys scrum was penalised and Elwood kicked the penalty to reduce the Welsh lead to 16-13 at half-time.
Connacht started the second half at break-neck speed, with skipper Tim Allnutt leading the way.
The centre produced a searing break in midfield to allow hooker Bernard Jackman to canter over the line, pushing away a half-hearted tackle by Durston to give Elwood a simple conversion.
Under pressure now, the Osprey's handling disintegrated and Connacht seized on the errors, Mike McCarthy scooping a loose ball and showing impressive pace for a second row to go 50 yards for the try.
Elwood missed his first place-kick of the night with the attempted conversion, but Connacht still led 25-16.
With just over 60 minutes gone, Connacht were reduced to 14 men when Robinson, somewhat harshly, was sin-binned for kicking away a ball at the ruck.
It didn't faze the Irishmen though, who marched upfield and despite being a man down still produced an overlap for replacement Conor McPhillips to score an unconverted try - the fourth touchdown claiming a bonus point.
Connor and Durston did pull back a penalty each, the excellent Connor having - slightly puzzlingly - been replaced by Gavin Henson just before full-back Durston made it 22-30.
But replacement Connacht full-back Mark McHugh restored the Irish lead to a match-winning 11 points with a long-distance penalty, after Elwood decided it was out of his range.
Ospreys coach Lyn Jones blamed the defeat on the failings of his front five, where he is missing eight players to injury or international calls.
"We know where we are weak and so does everyone else, but we are trying to paper over the cracks," said Jones. "I was pleased with many of the other aspects of our game, though."
Ospreys: Adrian Durston; Dave Tiueti, James Storey, Scott Gibbs (capt), Gareth Morris; Shaun Connor, Andy Williams; Paul Jones, Chris Wells, Andrew Millward, Andy Newman, Lyndon Bateman, Gavin Thomas, Richard Pugh, Nathan Bonner-Evans.
Replacements: Gavin Henson, Rhodri Wells, Alun Wyn Davies, Cai Griffiths, Andrew Clatworthy, Luke Tait, James Bater.
Connacht: David Hewitt; Ted Robinson, Matt Mostyn, Tim Allnutt (capt), Wayne Munn; Eric Elwood, Mike Walls; Dan McFarland, Bernard Jackman, Adrian Clarke, Damian Browne, Mike McCarthy, John Muldoon, Paul Neville, Michael Carroll.
Replacements: Henry Bourke, Fabian Boiroux, Andrew Farley, John O'Sullivan, Conor O'Loughlin, Conor McPhillips, Mark McHugh.
Referee: David Changleng (Scotland).