A late Harry Williams try proved decisive as Exeter Chiefs came from 14 points behind to overcome Worcester Warriors.
England international Ben Te'o has joined Toulon until November to provide cover for players leaving the Top 14 side for the World Cup.
Having spent six successive years in the top flight, Newcastle Falcons were relegated from the Premiership on Saturday.
Gloucester returned to the play-offs for the first time since 2011 despite losing to Worcester Warriors, who sealed Premiership safety.
Jack Singleton, who came through Saracens' academy, is to return to Allianz Park next season on a three-year deal.
England international Ben Te'o is one of eight players who will be leaving Sixways at the end of the Premiership season.
There was a tense finish at Sixways Stadium as Harlequins won by just two points over Worcester Warriors in the European Challenge Cup.
Josh Adams will be a Cardiff Blues player from next season after agreeing a move from Worcester Warriors.
Brett Connon held his nerve with a late penalty to give Newcastle victory at Wasps, while Exeter also did the Falcons a favour.
Newcastle Falcons closed the gap on second-bottom Worcester Warriors to five points with a 17-6 victory in the Premiership on Sunday.
Worcester Warriors eased their relegation fears with a third victory of the season over Leicester Tigers, who have lost five in a row.
Calum Clark and David Strettle scored second-half tries as Saracens rallied to beat Worcester Warriors, while Harlequins held off Wasps.
Cobus Reinach and Luther Burrell scored intercept tries and Dan Biggar had a good outing at the tee in a comfortable win for Northampton.
There were wins for Pau and Grenoble over Worcester Warriors and Agen respectively in the European Challenge Cup.
There were Premiership wins for Newcastle Falcons and Worcester Warriors on Friday, with the former moving off the foot of the table.
Teenage lock Joel Kpoku came off the bench to give Saracens a seventh Premiership wins out of seven, which put them back at the... Read more