Rea has a 30-point lead over Chaz Davies at the top of the standings.
The Kawasaki rider becomes the first rider since Englishman Neil Hodgson in 2003 to win the first four races of the season.
Having dominated practice and qualifying and won race one on Saturday, Rea secured a convincing victory in the second event of the weekend.
The race was initially red-flagged after Aprilia rider Lorenzo Savadori crashed out, depositing oil and debris from his machine.
Rea was forced to start from ninth because of the new reverse grid positions rules introduced for World Superbikes in 2017 but soon made his way to the front, before the race was brought to a premature halt.
Back in pole for the 16-lap restart, the County Antrim man pulled away from his rivals to chalk up the 42nd triumph of his career in the series, including 12 doubles.
Rea has now won five of the six races held over the Chang International Circuit since the Thai round was introduced in 2015.
“I’m so happy. I made a good start and managed to get clean away and stay in a rhythm. I’m feeling good with the bike,” said Rea.
As he did on Saturday, Sykes overtook Marco Melandri on the final corner to clinch second spot, with Alex Lowes, Jordi Torres and Welshman Davies, who slid off in the original race, completing the top six.
Eugene Laverty finished 15th and now lies 11th in the championship, with 15 points.
The next round will be held in Aragon at the start of April.
|World Superbike Championship 2017|
|1. Jonathan Rea (GB)||Kawasaki||100|
|2. Chaz Davies (GB)||Ducati||70|
|3. Tom Sykes (GB)||Kawasaki||62|