Tsukakoshi came out on top in a pulsating battle with Toshiki Oyu in the closing stages of the 300km race following an earlier red flag.
That was after Naoki Yamamoto suffered a major crash in the Kunimitsu Honda exiting the final corner, after contact with the Kondo Racing Nissan GT300 car, which led to the race being paused for around 50 minutes.
Yamamoto was reported to be conscious after the incident and able to move his arms and legs, but no further information was known about his condition at the time of publication.
The pole-winning #8 ARTA Honda NSX-GT of Tomoki Nojiri and Oyu finished seven seconds in arrears of the Real NSX in second, just holding on ahead of the NISMO Nissan of Tsugio Matsuda and Ronnie Quintarelli.
Tsukakoshi and Matsushita now find themselves only a single point away from the lead of the standings, which is held by NDDP Nissan pair Katsumasa Chiyo and Mitsunori Takaboshi, with two races to go.
In GT300, Team UpGarage pair Takashi Kobayashi and Shun Koide scored a dramatic victory in their Honda NSX GT3 as the leading Saitama Toyopet Toyota GR Supra appeared to run out of fuel at the finish line.
Source: Autosport