Leaders Quins stung by Wasps
Wasps beat Aviva Premiership leaders Harlequins 17-16, while their were also wins for Gloucester, Leicester, London Irish and Bath
Wasps' deadly wing duo Tom Varndell and Christian Wade both struck to sink Harlequins as Nick Evans missed the chance to pinch victory for the champions at the death.
Varndell and Wade both scored first half tries and while Quins romped back, Evans missed a 78th-minute penalty which would have almost certainly won it for his side and extended their winning run to 11 matches.
Evans downed Wasps at the death in a 42-40 thriller at Twickenham on the first day on the season but he missed out this time.
Instead, Wasps bounced back into the top four with a first win at the Stoop in six years, and their second away win of the campaign.
Two Jonny May tries saw Gloucester move above Northampton as they inflicted a 27-11 defeat on their hosts.
It was Northampton's third defeat at Franklin's Gardens in the league, and it was down to some magnificent Gloucester defence as Saints were twice stopped on the line and held up over it once, with the back row duo of Sione Kalamafoni and Akapusi Qera superb.
May conjured a piece of magic in the first half and then pounced on a dropped ball for a 70 metre try for his second. After that it was dogged defence from Gloucester who took revenge for losing at home to Northampton at the start of the season.
Leicester continued their relentless charge towards a play-off place against London Welsh thanks largely to the goal kicking of departing fly-half George Ford in a 28-12 success.
Publicly criticised for his decision to depart Welford Road this summer, Ford produced a near-faultless display in the absence of England international Toby Flood with 13 points to keep Welsh at arm's length.
Adam Thompstone scored a first-half try, with Niall Morris and Dan Bowden touching down for the Tigers after the break, while Gordon Ross scored 12 points for the Exiles.
Tom Homer kicked 19 points London Irish bagged a crucial win in their fight against relegation by beating Saracens 29-16.
The game was finely poised at the break with Homer and Sarries' Charlie Hodgson trading three penalties each.
But the Exiles put in an outstanding second half display and tries from Shane Geraghty and Ofisa Treviranus, aided by the accurate kicking of their full-back, sealed a potentially season-defining win.
David Strettle briefly gave the visitors hope, but it wasn't to be for the top-four contenders.
A fluent attacking performance from Bath earned them a welcome bonus-point 32-9 victory win over Worcester in the battle between eighth and ninth.
It was not quite enough to overtake Exeter - the two West Country sides are now level on points - but it was Bath's fifth win in succession in all competitions, suggesting they are building momentum for an assault on several fronts in the last two months of the season.
First-half tries from Peter Stringer and hooker Rob Webber gave Bath a slightly shaky 13-9 lead but they ran Worcester off their feet in the second half with further tries by wings Tom Biggs and Horacio Agulla (two).
Worcester's only points were three first-half penalties from Danny Gray.