Noah Caluori scored four tries as Saracens overwhelmed Newcastle 73-14 at StoneX Stadium.
Former England captain Jamie George will retire from rugby in 2027 after signing a new one-year contract at Saracens.
Harlequins defied their abysmal domestic form to stun La Rochelle 27-17 at Stade Marcel Deflandre and secure home advantage in the Champions Cup round of 16.
Northampton Saints were brought back down to earth after they suffered a 50-28 loss away to Champions Cup holders Bordeaux in a repeat of last season's final.
Adam Radwan scored two tries as Leicester kept in contention for a play-off spot with an impressive 36-28 win over Saracens.
Northampton stunned the Prem Rugby champions Bath with a devastating display of running rugby featuring a hat-trick of tries by freewheeling England back Tommy Freeman.
Munster bounced back from a disappointing defeat to Bath last week to comprehensively beat Gloucester 31-3 in the Champions Cup at Páirc Uí Chaoimh in Cork.
An astonishing start which saw Bath 28-0 ahead inside 19 minutes proved crucial as the Prem side saw off Munster 40-14 in their Champions Cup opener.