La Rochelle kept their hopes of progressing in the European Champions Cup alive by beating Sale Sharks, while Harlequins edged out Bath.
Sam Underhill, Jack Walker and Max Wright have all signed three-year contracts to remain at Bath.
Five tries in each half saw Premiership basement side Saracens make light work of thumping Worcester Warriors on Saturday.
Munster put in a monumental effort, but Leinster's defence refused to buckle at Thomond Park.
Northampton Saints defeated Gloucester in a barnstorming contest at Franklin's Gardens, while Sale Sharks overcame Bath in the Premiership.
Bath arrived at the Madejski Stadium with no form to speak of, but Stuart Hooper's side stormed to a comprehensive win against London Irish.
Brothers Joe and Sam Simmonds were influential as Exeter Chiefs moved to the brink of a quarter-final spot in Europe.
Bath were no match for a classy Clermonth Auvergne in Friday's European Rugby Champions Cup clash.
In their first Premiership match since accepting a 35-point deduction for breaching salary-cap rules, Saracens defeated Bath 25-12.
Anthony Watson's knee injury is not as serious as first feared, but he may not play again this year.