The Ospreys claimed only their second Pro14 win over the season at the expense of high-flying Ulster in a stormy Swansea.
Luke Price booted the Ospreys to a stunning 26-24 victory over Ulster and Leinster maintained their 100 per cent Pro14 record by defeating the Cheetahs on Saturday.
The Ospreys had only one Pro14 victory to their name in the competition against Benetton Treviso back in October, but doubled their tally with a shock success as Storm Dennis battered Swansea.
Ulster, second in Conference A behind Leinster, came from 23-10 down to take a one-point lead courtesy of tries from Matt Faddes and Stuart McCloskey, Bill Johnston converting both scores in the space of nine minutes.
Scott Otten had scored a try in each half for the home side after Owen Watkin's five-pointer, but they looked set for more agony until Price split the posts with his third penalty of the match five minutes from time to lift the gloom.
The Leinster juggernaut rolled on at the RDS Arena, where Will Connors grabbed a double and there were also tries for Michael Bent, Ronan Kelleher and Rhys Ruddock in a commanding 36-12 victory.
Luan de Bruin and Aidon Davis crossed for the Cheetahs, third in Conference A, but they were soundly beaten by the defending champions.
Edinburgh completed a double over the Scarlets with a 14-9 win in Llanelli to return to the summit of Conference B, Duhan van der Merwe and Matt Scott scoring the only tries.
Connacht thumped Cardiff Blues 29-0, while the encounter between the Dragons and Treviso, due to be played at Rodney Parade, was called off due to the extreme weather conditions
Watch: Sean Cronin's hiccup at the lineout