Michael van der Mark secured his second win in two days at Donington as World Superbike champion and series leader Jonathan Rea came in third.
Rea edged in front with seven laps left before Dutchman Van der Mark made his decisive move two laps later and won comfortably on his Yamaha.
Turkish rider Toprak Razgatlioglu passed Rea on the final lap to take second place.
The Northern Irishman, though, extended his championship lead to 64 points.
England's Leon Haslam was forced out on lap two while lying second and it soon developed into a three-way battle between his compatriot Alex Lowes, Van der Mark and Rea.
Rea pushed through to lead on his Kawasaki and he was on course to chalk up a record 60th series victory.
But the weekend belonged to 25-year-old Van der Mark, who followed up his maiden World Superbike win on Saturday by cruising to race two success.
Razgatlioglu became the first Turkish rider to make a World Superbike podium as he moved past Rea to finish runner-up.
Lowes had to settle for fourth while Wales' Chaz Davies and England's Tom Sykes completed the top six.
"I can't believe it - Saturday was like a dream and I was scared to think of a double but we did it," said Van der Mark.
"I stayed calm and kept my head down. I managed to pass Jonathan and go on to win."
Van der Mark is now tied third in the 2018 standings, 18 points behind Davies while Rea holds a commanding lead as he chases a fourth straight title.
"It was really difficult to make the front and I ran into arm-pump issues at the end," said Rea.
"The guys gave me a great bike which was ready to win, but I wasn't."
|World Superbike Championship 2018 standings|
|1. Jonathan Rea (GB)||Kawasaki||245|
|2. Chaz Davies (GB)||Ducati||181|
|3. Michael van der Mark (Ned)||Yamaha||163|
|4. Tom Sykes (GB)||Kawasaki||163|
|5. Marco Melandri (Ita)||Ducati||136|
|6. Xavi Fores (Spa)||Ducati||124|