Sale Sharks can seal the final Premiership play-off place with a win after Saracens stormed back to deny Bath victory.
A bonus-point 40-3 victory over Leicester Tigers boosted Bristol's hopes of finishing in the Premiership's play-off places.
Saracens and Exeter Chiefs will go their separate ways at the end of the season, but a second-string battle was a reminder of their rivalry.
Leicester Tigers were thrashed by Wasps while Sale Sharks held off Saracens in Wednesday's Premiership matches.
Just under 3,000 fans returned to see Harlequins lose to Bath, while Owen Farrell saw red for a high tackle as Saracens lost against Wasps.
Wasps lost four players to injury in the first half at The Rec and trailed by 13 points, but roared back to claim a battling victory.
Worcester Warriors won their first game of 2020 on Wednesday, while Bath's strong second-half display led them to a third win a row.
Harlequins were unable to recover from a dominant first-half display by rivals Saracens at Allianz Park.
Leaders Exeter Chiefs resumed the season with a win over Leicester Tigers, while Bristol left it late to down Saracens.
Rob Simmons is on his way out of the Waratahs after agreeing a deal with ambitious Premiership club London Irish.