Gloucester led 16-13 after a frenetic opening half thanks to tries from captain Gareth Delve and flanker Adam Eustace, plus a penalty apiece from fly-half Nicky Robinson and full-back Freddie Burns. Cardiff's points came courtesy of a Xavier Rush score plus eight points from Sweeney's boot.
Burns and Sweeney traded penalties early in the second-half before Sam Norton-Knight glided over to put Cardiff back in front but two late penalties from Carlos Spencer looked to have given the Cherry and Whites a first win in five games, only for Sweeney, who kicked 16 points in total, to hold his nerve in the dying seconds.
First-half tries by David Lemi and Mark Van Gisbergen combined with the boot of Dave Walder to earn
Wasps, who took this match seriously by playing a close-to-full-strength team, were 18-10 up at the break thanks to the touchdowns by two of their back three.
Walder had kicked a conversion and two penalties by then and he added another three-pointer after the interval to steer the visitors home.
Peter Hewat went over for a brace of tries for Irish, one either side of half-time, but they could not recover despite late pressure.
Strettle, released to play for his club when Martin Johnson reduced his original 32-man squad for the Twickenham clash with
But clearly struggling, he was replaced by George Lowe nine minutes later in his side's opening pool match at The Stoop.
Harlequins added a further try from lock George Robson and a penalty and conversion from fly-half Rory Clegg.
The Welsh side replied with tries from centre Gareth Maule, left-wing Andy Fenby and a penalty and conversion from number 10 Rhys Priestland.
Neil Back guided a youthful
Debutant Joe Ford, son of
Scott Armstrong and Scott Mathie also crossed for Leeds, while Ford's younger brother George kicked a penalty and converted tries from William Hurrell and Tom Armes for Leciester.
The Sharks were always on the back foot in Gwent after Dragons fly-half Shaun Connor crossed for the game's opening try when he ghosted through some non-existent Sale defence for a converted try.
Former Wales flanker and captain Jones said: "We did not respect the Dragons. We talked all week about coming down here and giving them the respect they deserve and to give away seven points like that in the first two minutes just speaks volumes."
Rob Miller put the Falcons ahead with his boot, but Willie Walker replied for Warriors before wing Miles Benjamin crossed to give the hosts the lead.
After another Miller penalty, Walker knocked over a drop-goal and converted scores from Tom Wood, Ollie Frost and Jake Abbott as Worcester romped to victory.