Kawasaki rider Rea beat Bautista by a scant 0.103 seconds to retake the championship lead from the Ducati rider, with poleman Razgatlioglu dropping away from the lead battle in the closing stages.
Razgatlioglu converted pole into an early lead, but Rea soon picked off the reigning champion's Yamaha teammate Andrea Locatelli to move into second.
On lap three of 21, Rea dived up the inside of the final chicane to take the lead, seemingly controlling the pace thereafter with a six-rider train forming at the head of the pack featuring the works Yamaha, Kawasaki and Ducati riders.
Bautista was fifth behind the second Kawasaki of Alex Lowes at this point, but managed to find a way by Lowes and Locatelli on consecutive laps before Lowes suffered a race-ending mechanical problem on lap 11.
With Locatelli dropping away from the lead pack, the race became a three-way battle from this point onwards, with Razgatlioglu managing to take the lead back from Rea at the end of lap 13.
But the Turkish rider couldn't escape at the head of the field, and Rea was able to regain the advantage with a daring late-braking move into Turn 1 on lap 16.
Bautista passed Razgatlioglu several corners later to take over as Rea's main challenger, and on lap 18 the Spanish rider briefly moved ahead with a pass at the high-speed Ruskenhoek chicane - only for Rea to reply immediately and go back around the outside at the Stekkenwal right-hander.
Once back ahead, Rea resisted Bautista's advances to secure his 16th career WSBK win at Assen.
Razgatlioglu had to settle for third, a second back from the leaders, with teammate Locatelli coming home a lonely fourth nine seconds further behind.
Following a crash for Ducati's Michael Ruben Rinaldi in the closing stages, Iker Lecuona took his best WSBK finish so far in fifth for Honda, followed by top BMW rider Loris Baz and Philipp Oettl on the satellite GoEleven Ducati.
Garrett Gerloff dropped back in the early stages aboard the GRT Yamaha, having gone for a harder rear tyre option than the SCX compound favoured by the majority, but picked off Scott Redding on the final lap for eighth.
Redding still came away with his best result as a BMW rider in ninth, while teammate Michael van der Mark was 13th in his first race back from injury.
Puccetti Kawasaki man Lucas Mahias picked up the final point in 15th despite a last-lap crash, just holding off Pedercini Kawasaki's Leon Haslam, called up late as a replacement for Loris Cresson this weekend.
Assen WSBK - Race 1 results:
| Cla | # | Rider | Bike | Gap |
|---|---|---|---|---|
| 1 | 65 |
 Jonathan Rea | Kawasaki | |
| 2 | 19 |
 Alvaro Bautista | Ducati | 0.103 |
| 3 | 1 |
 Toprak Razgatlioglu | Yamaha | 1.014 |
| 4 | 55 |
 Andrea Locatelli | Yamaha | 9.712 |
| 5 | 7 |
Iker Lecuona | Honda | 17.451 |
| 6 | 76 |
 Loris Baz | BMW | 17.983 |
| 7 | 5 | Philipp Oettl | Ducati | 22.002 |
| 8 | 31 |
 Garrett Gerloff | Yamaha | 24.545 |
| 9 | 45 |
Scott Redding | BMW | 25.118 |
| 10 | 47 |
Axel Bassani | Ducati | 26.938 |
| 11 | 97 |
Xavi Vierge | Honda | 35.566 |
| 12 | 23 |
Christophe Ponsson | Yamaha | 41.901 |
| 13 | 60 |
 Michael van der Mark | BMW | 41.967 |
| 14 | 2 |
Roberto Tamburini | Yamaha | 42.014 |
| 15 | 44 |
Lucas Mahias | Kawasaki | 45.699 |
| 16 | 91 |
Leon Haslam | Kawasaki | 45.882 |
| 17 | 3 |
 Kohta Nozane | Yamaha | 45.972 |
| 18 | 29 |
 Luca Bernardi | Ducati | 47.975 |
| 19 | 36 |
 Leandro Mercado | Honda | 48.144 |
| 20 | 35 |
 Hafizh Syahrin | Honda | 58.169 |
| 21 | 52 | Oliver Konig | Kawasaki | |
| 21 |
Michael Ruben Rinaldi | Ducati | ||
| 22 |
Alex Lowes | Kawasaki | ||
| 16 |
Gabriele Ruiu | BMW | ||
| View full results | ||||
