Race one saw his closest opposition, front row starter Sota Ogawa, stall and drop back, leaving Sawa to claim the win ahead of Miki Koyama and Yoshiaki Katayama.
Race three did not offer much change: Sawa was once again the class of the field, gapping Ogawa and Koyama by over 20 seconds.
Race two saw only four drivers reach the finish, as "Hirobon" did not start and Katayama collided with Takashi Hata and Yuki Tanaka.
Koyama stayed clear of any incidents, winning again, ahead of debutant Kazuki Oki and gentleman driver Masaru Miura.
The last race was a calmer affair, with Koyama once again converting pole into an unchallenged victory ahead of Ogawa and Katayama.
[15] Round four at Sportsland Sugo saw Ogawa, Oki and Koyama share poles in qualifying.
Ogawa then overtook Koyama and closed up to Oki, but had to retire his car after fighting heavily for the lead.
Race three was controlled by Koyama who led from lights to flag, while Oki had a bad start that saw him get passed by Ogawa.
Race two saw another slow start by Koyama, she dropped back to third but was able to regain second place and then also take the lead from Okusa.
Koyama's race two victory saw her seal the championship title, with her lead now an unassailable 79 points ahead of the final round.
Ogawa managed his lead until the finish, with Koyama behind him and gentleman driver Takashi Hata completing the podium.
Entry numbers were back down to single digits, as the championship continued its struggle to attract more drivers for a third year round.