Tom Sykes won the opening World Superbike race at Donington, while third-placed Jonathan Rea moved further clear at the top of the championship.
It was a seventh straight Donington victory for the English rider, who finished 2.8 seconds clear of Italy’s Davide Giugliano after a close battle.
Rea goes into Sunday’s second race with a 58-point advantage over closest challenger Chaz Davies.
Welshman Davies crashed out and is just three points ahead of Sykes.
A mistake saw Sykes drop to fourth but he eventually overtook Giugliano, although the Italian pushed him all the way.
Defending champion Rea started the day with a 42-point lead and the Northern Ireland rider completed the podium, with fellow Briton Leon Camier fourth and American Nicky Hayden back in fifth.
A late error resulted in IodaRacing’s Lorenzo Savadori, who won the STK1000 race at Donington last year and who began on the front row, coming in sixth.