However, tries from Rhys Gill, Ernst Joubert and full-back Chris Wyles cancelled out those of Ireland international Tommy Bowe and Ashley Beck in reply for the Ospreys.
Other English hopefuls staking a claim for next year's tournament were Northampton centre Jamie Elliot, who helped himself to two tries in Saints' 41-22 defeat to Castres, while fly-half Freddie Burns kicked three penalties to squeeze Gloucester to a 14-10 victory over Connacht.
Elsewhere, Scotland Joe Ansbro touched down as London Irish won 34-14 at Racing Metro.
The French side led 14-10 at half-time but Ansbro was joined on the scoresheet by Jonathan Spratt and Adam Thompstone with a double for a comfortable victory.
Meanwhile, four Ronan O'Gara penalties and a Niall Ronan try helped Munster to a 17-14 victory over Scarlets, who themselves crossed once through Aaron Shingler and had Rhys Priestland and Stephen Jones to thank for three penalties between them, while Treviso won 30-26 against Biarritz.