Harry Byrne's goal-kicking proved the difference as an error-strewn Leinster held off a determined Leicester to claim a 23-15 victory in the Investec Champions Cup.
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.
Exeter came from 26-6 down to secure a dramatic 27-26 win and inflict a rare home defeat on Sale as the Gallagher PREM resumed.
Leicester Tigers eked out a 36-35 win against Sale Sharks as Bath, Harlequins and Exeter all won by big scorelines in Saturday's Gallagher Prem action.
Billy Searle's penalty with the final kick of the game secured Leicester a dramatic 22-20 victory over Gallagher Prem champions Bath.
Playing rugby has no causal link to motor neurone disease, according to an expert in the incurable muscle-wasting condition.
Leicester staged an incredible fightback to beat Harlequins, whilst Exeter beat Newcastle, and Saracens took control of Bristol.
Bath clinched their first Premiership title for 29 years dating back to 1996 after holding off a late Leicester Tigers fightback to win 23-21 at Twickenham.