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.
Nojiri led the start of the race from pole, quickly building a cushion at the head of the field ahead of Quintarelli and Matsushita. By the end of lap 17, Nojiri's advantage was out to more than 12 seconds, but it was back down to less than 10 by the time the pitstop phase began on lap 28 of 84.
The first of the three leaders to pit was Quintarelli, who came in to hand over to Matsuda on lap 30, while Nojiri stayed out until lap 32 and Matsushita enjoyed a single lap in the lead before pitting on lap 33. But the Real crew gained a significant amount of time during the pitstops, with the result that Tsukakoshi rejoined ahead of Oyu to maintain the lead even while he got his tyres up to temperature.
Meanwhile, the SARD Toyota of Yuhi Sekiguchi and the Impul Nissan of Bertrand Baguette cycled through to first and second by virtue of leaving their stops later, but neither had pitted by the time of Yamamoto's crash at the end of lap 39.
Sekiguchi led the field back to green as the race resumed on lap 45, but because the safety car had picked up the leader prior to the stoppage, Tsukakoshi, Oyu and Matsuda were able to rejoin at the back of the queue and gain almost a whole lap on the field.
Tsukakoshi initially held firm but couldn't shake off Oyu, who made use of lapped traffic to set up a move through the final corner and along the start/finish straight at the end of lap 52.
When Sekiguchi made his stop that lap, Oyu, Tsukakoshi and Matsuda retook the top three positions. Oyu built a three-second lead over Tsukakoshi, but appeared to start struggling as the race wore on, allowing both Tsukakoshi and Matsuda back into the frame.
Tsukakoshi was clearly the faster of the two Honda drivers in clear air, and at the end of lap 76 another moment with lapped traffic at the last corner gave him the chance he needed to repass Oyu for the lead. From there, Tsukakoshi stretched a lead of seven seconds by the chequered flag to score he and Matsushita's first win of the season and their second as a duo following last year's Autopolis round.
Matsuda settled for third place behind Oyu, while the SARD Toyota GR Supra of Sekiguchi and Yuichi Nakayama was a distant fourth, a massive 58 seconds behind at the finish but having had the chance to make a pitstop while essentially a lap ahead of fifth place and back.
The Impul Nissan shared by Baguette and Kazuki Hiramine stopped on lap 44 as the safety car came in, Hiramine initially slipping down to the foot of the top 10 on cold tyres. But on fresher rubber, the #1 car was able to steadily claw back positions to complete the top five.
Kondo Racing pair Daiki Sasaki and Kohei Hirate made it three Nissan Zs in the top six, ahead of a trio of Toyota crews, with Rookie Racing leading home the #36 TOM'S and the Racing Project Bandoh GR Supras.
The championship-leading NDDP Nissan scored a single point in 10th to take Chiyo and Takaboshi's points tally for the year to 50, with Tsukakoshi and Matsushita on 49 and TOM'S pair Sho Tsuboi and Ritomo Miyata on 48.
GT300: UpGarage steals dramatic win from Saitama Toyopet
In the GT300 class, Honda squad Team UpGarage scored its third win of the season, putting drivers Takashi Kobayashi and Shun Koide into a commanding position in the title race.
Carrying 100kg of success ballast, Kobayashi looked on course to bring home the UpGarage Honda NSX GT3 second behind the Saitama Toyopet Toyota GR Supra of Hiroki Yoshida and Kohta Kawaai, which had jumped up the order during the pitstops after only changing two tyres.
But with the chequered flag in sight, Yoshida dramatically slowed, frantically weaving as he neared the finish line, allowing Kobayashi to pass for the victory by just eight tenths of a second.
Kobayashi and Koide's third win of 2023 puts them 15 points clear in the title race ahead of Yoshida and Kawaai, and marks the first time any GT300 squad was won three times in one season since 2011.
