Northampton Saints and Glasgow Warriors did all they could to stay in the European Champions Cup, while Ulster are definitely through.
La Rochelle kept their hopes of progressing in the European Champions Cup alive by beating Sale Sharks, while Harlequins edged out Bath.
It was a night to forget for Harlequins on Friday, as they were thrashed by a rampant Sale Sharks side in Premiership action.
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.
Saracens won a fifth straight Premiership match, though they are still far behind Leicester Tigers, who were defeated by Exeter Chiefs.
Juan Imhoff scored two of Racing 92's six tries as they beat Ospreys 40-27 to increase their lead at the top of Pool 4.
There were seven tries in Leinster's 43-16 European Champions Cup win over Northampton Saints as they made it 10 victories from 10.
London Irish battled to claim a draw at Bristol Bears despite seeing Ollie Hoskins sent off on the stroke of half-time.
Experienced England full-back Mike Brown will miss the rest of the Premiership season, Harlequins have confirmed.
Ospreys were no match for Saracens on Saturday, while Exeter Chiefs were among the other European Champions Cup winners.
Ireland centre Garry Ringrose was the star of the show as Leinster started their bid to regain the Champions Cup with a bonus-point win.
A looming points deduction would see Saracens facing a Premiership relegation battle this season, but they defeated Gloucester on Saturday.
Chris Robshaw says "the pinnacle of English rugby is illegal" after Saracens were found to have breached the salary cap.
Taqele Naiyaravoro impressed again as Northampton maintained their winning start to the Premiership season on Friday.
Northampton Saints and Gloucester followed up narrow away wins on the opening weekend by easing to home successes in the Premiership.