From second on the grid, Lawson defeated poleman Tadasuke Makino in the 41-lap race, jumping ahead during the mandatory pitstop phase.
The Team Mugen driver came in for his stop on lap 11 of 41, easily resuming ahead of those that had changed tyres when the pit window opened the previous lap, before Makino pitted from the lead at the end of lap 12.
While Makino initially resumed ahead, on cold tyres he was powerless to fend off Lawson, who swept past at the Turn 3 left-hander before going on to win by 4.4 seconds.
Looking back on the race, Lawson admitted that a second practice session on Sunday morning in which he was only seventh-fastest meant he went into the race unsure if he would be able to convert his front-row starting position into victory.
The New Zealander said changes made to his Mugen machine to suit the somewhat cooler-than-expected but still muggy conditions for the race proved vital.
“Race pace has generally been strong, especially here, but we weren’t confident with the conditions at all, to be honest,” Lawson told Motorsport.com.
“We weren’t the strongest on race runs in the morning, and we thought it might be tough. Normally we are strong in FP2 and that gives us confidence for the race but this time I didn’t feel that.
“We changed the car quite a bit, and when you do that, it’s stressful because you don’t know if it’s going to work or not.
“[In the first stint] I was pushing and I could only get within a second [of Makino]. I tried to back off and come back, but I couldn’t get any closer than that. The undercut worked well for us, though.
“Our out laps have been good this year. From the last corner my eyes were glued to the pit exit, and then when I saw him come out [just ahead] I realised we’d be ok.”
Lawson heads into the final three races of the season just a single point behind championship leader Ritomo Miyata, who finished third from fifth on the grid.
He will tackle Motegi for the first time next month before the season concludes with a double-header at Suzuka in late October.
Asked what he feels the key to title success will be, Lawson replied: “Executing qualifying is massively important. We did that this weekend and we need to look at what we did and make sure we repeat that.
“If we put ourselves in a position to be at the front in qualifying, we have good race pace. But it’s so hard to fight from behind. You can easily get stuck like I did at Sugo. We can’t afford to be in that position again.
“We still have a few races left, and Miyata has been extremely consistent this year, so it’s going to be tough for sure.”
