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.
Exeter Chiefs reached their first European Champions Cup final at Toulouse's expense after Racing 92 dumped Saracens out.
Holders Saracens are a win away from the Champions Cup final after beating Leinster, while Racing 92 powered past Clermont Auvergne.
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.