England captain Owen Farrell was sent off as Saracens were downed 28-18 by high-flying Wasps, while a limited crowd saw Harlequins well beaten by Bath at The Stoop.
Sarries named a stronger side on paper than Saturday's opponents at Allianz Park and the game was poised at 15-15 after tries from ex-Wasps star Elliot Daly and Sean Maitland, plus five points from Farrell's boot, were answered by five penalties from the classy Jimmy Gopperth.
But Farrell saw red after catching Charlie Atkinson in the face with his left shoulder just after the hour and Tom Willis powered over with 10 minutes to go, while Gopperth finished with 23 points on his 100th Wasps appearance.
Around 2,700 fans were in attendance for Quins' home clash with Bath as part of a test event as the United Kingdom aims to get spectators back at sporting events amid the coronavirus pandemic.
But having fans back did little to inspire Quins as Bath earned a 41-27 bonus-point win that moved them fifth, with Ruaridh McConnochie scoring in each half and Rhys Priestland kicking 21 points.
Sale Sharks regained second spot in the table as Manu Tuilagi scored against his former club Leicester Tigers in a 40-31 triumph at Welford Road.
There were seven tries in total in a high-scoring game, in which AJ MacGinty, Jono Ross and Denny Solomona also registered for Sale.
Rounding out the action, Gloucester picked up a bonus point with a 36-23 victory over London Irish.