London Irish put an end to both their losing streak and the Ospreys' Heineken Cup hopes on Sunday with a 24-12 win at Madejski Stadium.
Irish went into the game looking to end a run of 10 consecutive defeats, their worst in four years, and tries from Sailosi Tagicakibau and Topsy Ojo saw them do so.
And there was further bad news for Ospreys, and Wales ahead of the Six Nations, with Adam Jones taken off at half-time after suffering what looked like an injury to his left shoulder when a scrum collapsed.
Irish broke the deadlock thanks to Dan Bowden's 16th-minute penalty, but Ospreys responded immediately as Irish went offside to deny a try-scoring opportunity. Dan Biggar scored the equalising penalty on 18 minutes.
But Irish surged upfield again, and this time exposed Ospreys defence when Delon Armitage switched a pass to his left to send Tagicakibau racing up the line for a try.
After a very positive start, Ospreys were now on the back foot as Irish went up through the gears, and it needed quality defending by a succession of Wales internationals to protect their line.
But then Ospreys collapsed a scrum on their own put-in, gifting Bowden the chance to increase the Irish lead on 28 minutes.
Referee George Clancy penalised Matt Garvey for ball-killing at a ruck three minutes later, and Biggar punished the offence with a 40-metre goal.
Then Ospreys were penalised by the official for a similar offence after 38 minutes, which gave Bowen the chance to regain the eight-point lead at 14-6.
No sooner had the second half begun than Ospreys were deep in trouble.
One minute in and Bowden made a break and Tagicakibau moved the ball left, releasing Ojo who sped round behind the posts, Bowden converting.
Biggar kicked his third goal on 44 minutes, but missed a second chance two minutes later as Ospreys threw everything into attack.
Irish had territory and opportunities to increase their lead, but failed and then handed Biggar another kick at goal through indiscipline. But he again fired wide.
With rain now swirling down upon the Madejski Stadium, handling became difficult and both sides were guilty of knock-ons at the height of promising attacks.
Having squandered some decent leads during their 10-game run, Irish were guilty of blunders in the final quarter that had their supporters holding their heads. Armitage nearly cost a try by attempting to run a ball clear that had to be kicked, and turned it over.
Then another act of indiscipline handed Ospreys a lifeline which James Hook hammered over on 65 minutes.
But when Bowden was offered the same chance, he fired wide on 68 minutes, increasing the crowd's anxiety and reviving the Ospreys supporters.
Then Irish lost hooker James Buckland to a yellow card for ball-killing as Ospreys camped on their line.
Wave upon wave of attacks were repelled, but when it seemed Ospreys had to score, Clancy awarded Irish a penalty for Ospreys not releasing in the tackle.
And replacement fly-half Ryan Lamb sealed the win three minutes from time with an angled penalty from wide out on the left.
For London Irish:
Tries: Tagicakibau, Ojo
Pens: Bowden 3, Lamb
Pens: Biggar 3, Hook
Yellow card: Buckland (London Irish)
London Irish: 15 Delon Armitage, 14 Topsy Ojo, 13 Elvis Seveali'i, 12 Seilala Mapusua, 11 Sailosi Tagicakibau, 10 Dan Bowden, 9 Darren Allinson, 8 Chris Hala'Ufia, 6 George Stowers, 5 Matthew Garvey, 4 Nick Kennedy, 3 Faan Rautenbach, 2 James Buckland, 1 Alex Corbisiero.
Replacements: 16 Brian Blaney, 17 Dan Murphy, 18 Paulica Ion, 19 Bob Casey, 20 Jamie Gibson, 21 Adam Thompstone, 22 Ryan Lamb, 23 Alfredo Lalanne.
Ospreys: 15 Barry Davies, 14 Nikki Walker, 13 Tommy Bowe, 12 James Hook, 11 Richard Fussell, 10 Dan Biggar, 9 Mike Phillips, 8 Jonathan Thomas, 7 Marty Holah, 6 Jerry Collins, 5 Alun Wyn Jones (capt), 4 Ryan Jones, 3 Adam Jones, 2 Richard Hibbard, 1 Paul James.
Replacements: 16 Huw Bennett, 17 Duncan Jones, 18 Craig Mitchell, 19 Ian Gough, 20 Justin Tipuric, 21 Jamie Nutbrown, 22 Sonny Parker, 23 Lee Byrne.
Venue: Madejski Stadium, Reading
Referee: George Clancy