Kawasaki rider Rea managed to win the opening race of the weekend for only the second time in 2021, and for the first time since the Aragon curtain-raiser, despite his perfect record of pole positions this year.
From second on the grid, Yamaha rider Razgatlioglu was able to take the lead away from Rea into the first corner, but the reigning champion struck back just corners later to regain the advantage.
Razgatlioglu stuck with his rival and made another pass into Turn 1 on lap four of a planned 21, but once again the Turkish rider’s stint out front was short-lived as Rea snatched back the lead the next lap.
From there, Rea was able to steadily ease away from Razgatlioglu, who had to spend most of the race battling the Ducati of Redding for second.
Redding got ahead of Razgatlioglu on lap eight and looked set to challenge Rea for the lead, but by lap 11 Razgatlioglu had caught back up and repassed, allowing Rea some vital breathing space.
Second place changed hands several more times between Redding and Razgatlioglu, but it was Redding that was ahead when the race was red-flagged with two laps to go following a crash for Jonas Folger.
Rea earned his sixth victory of the season by three seconds over Redding, who in turn was only just over a tenth clear of Razgatlioglu.
Behind the lead trio, Michael van der Mark benefitted from several early crashes to finish fourth on the BMW on home soil.
Alvaro Bautista (Honda) was first to go down at Turn 7, followed by both Alex Lowes (Kawasaki) and Michael Ruben Rinaldi – who had passed his teammate Redding at the start to run third.
Andrea Locatelli meanwhile matched his best finish in WSBK for Yamaha in fifth place, while Garrett Gerloff recovered from his qualifying crash to take sixth on his GRT Yamaha from 21st on the grid.
Satellite BMW rider Folger had occupied sixth for much of the race and was still on course for his best result in WSBK in seventh when he crashed heavily on lap 19 at the Turn 6-7 complex, causing the race to be halted.
Folger was taken to the medical centre before being transferred to hospital for further assessment.
Likewise coming from the back of the field, Tom Sykes was seventh on the second factory BMW followed by the Honda of Leon Haslam and the privateer Ducatis of Chaz Davies and Axel Bassani.
Leandro Mercado was a creditable 12th aboard the MIE Honda in his first race outing since Aragon.