Katsumasa Chiyo and Mitsunori Takaboshi took full advantage of the mixed conditions in Sunday's 100-lap race in their Michelin-shod #3 Nissan Z, taking their first victory of the season by a commanding 43.9 seconds.
Two Honda NSX-GTs completed the podium, as ARTA duo Hiroki Otsu and Nirei Fukuzumi were best of the Bridgestone runners in second, followed by Team Kunimitsu pair Naoki Yamamoto and Tadasuke Makino in third.
The race was red-flagged after 68 of 100 laps when the Tsuchiya Engineering Toyota GR Supra GT300 car of Seita Nonaka stopped at the side of the track at Turn 3 and started going up in flames.
Such was the severity of the blaze that an initial safety car period gave way to red flags when it became clear that the marshals wouldn't be able to contain the fire immediately. Nonaka escaped uninjured.
The race resumed after an interlude of 50 minutes, in which time a rain shower doused the track, delaying the restart, but the full 100-lap distance was completed before the time limit was reached.
Victory in a topsy-turvy GT300 contest went the way of the #11 Gainer Nissan GT-R NISMO GT3 driven by Keishi Ishikawa and Ryuichiro Tomita.
Story of the race
Rain prior to the start meant that the race started behind the safety car for two laps before the green flag was shown on lap three, with all 15 GT500 cars starting the race on wet tyres.
The pole-sitting Kondo Racing Nissan of Daiki Sasaki led initially, but the NDDP car that started fourth in the hands of Chiyo was soon on the move, picking off the ARTA Hondas of Toshiki Oyu and Nirei Fukuzumi to move up to second.
On lap four, Chiyo passed Sasaki to take the lead, but the order would soon be reshuffled as the track dried and the GT500 runners came into the pits to complete their first refuelling stops and change to slick tyres, starting on lap 11.
Chiyo was one of the last cars to come in on lap 15, in the process dropping behind Fukuzumi's ARTA Honda and two cars that opted to short fill to gain track position, the Rookie Racing and SARD Toyota GR Supras.
It was the Rookie Racing car of Kazuya Oshima that had the pace at this stage, passing Fukuzumi to lead on lap 24, and that was how the order remained at the front until the safety car was called on lap 36 when the Max Racing Toyota GR Supra pulled off course on fire.
The race restarted on lap 41 with Oshima leading Fukuzumi, who was then passed by Yuhi Sekiguchi in the SARD car for second.
But Oshima pitted on lap 46 to hand over to Kenta Yamashita, with Sekiguchi coming in one lap later to make way for Yuichi Nakayama, with both cars now effectively locked into three-stop strategies.
Fukuzumi retook the lead as a result ahead of Chiyo, but the car on the move during this phase of the race was the #37 TOM'S Toyota of Ukyo Sasahara, who had made his way up from 12th on the grid to run third.
Chiyo was next of the leaders to stop on lap 56, handing over the NDDP Nissan to Takaboshi, followed by Fukuzumi next time by, with Hiroki Otsu taking over the ARTA machine. But both were vaulted by the TOM'S machine that Giuliano Alesi took over when Sasahara stopped on lap 59.
When the second pitstop phase was complete, Yamashita led Nakayama, but with both cars needing to stop one more time, with Alesi third ahead of Takaboshi and Otsu. That was how the order was when the race was neutralised by the safety car and then red-flagged for the Tsuchiya Supra's fire.
With more rain arriving just before the planned restart at 1610 local time, the restart was delayed, allowing the field to switch back to wet tyres. At 1630 the race resumed behind the safety car, and the green flags were shown on lap 72.
In ideal conditions for the Michelin wet tyre, Takaboshi made short work of the three Bridgestone-shod Toyotas ahead of him, passing Alesi, Nakayama and Yamashita in quick succession to lead on lap 75.
By lap 80, Takaboshi had put 12 seconds between himself and the field, virtually doubling his advantage in the next three laps, and finally ending up over 40 seconds clear when the chequered flag fell.
Meanwhile, Otsu surged through from fifth at the restart to run second, and was able to escape the chasing pack as Yamashita and Nakayama made their final stops and Alesi started dropping down the order.
The other ARTA Honda of Tomoki Nojiri, who took over from Oyu at the second round of stops, lost a strong chance of a podium with a spin exiting the final turn, shortly after which Nojiri pitted for slicks as the track dried.
That paved the way for Yamamoto to grab the final spot on the podium as he surged up the order in the closing stages, coming out on top in a late battle with the Dunlop-shod Nakajima Honda of GT500 rookie Kakunoshin Ota.
Likewise making serious ground late in the race was the #36 TOM'S Toyota, which had led the championship coming into the race and was carrying the stage two fuel flow restrictor.
Sho Tsuboi and Ritomo Miyata finally came through from the back of the field to finish fifth, beating Cerumo pair Hiroaki Ishiura and Yuji Tachikawa to end up as the top Toyota crew.
It means Tsuboi and Miyata now sit second in the championship, seven points behind new leaders Chiyo and Takaboshi.
Alesi finally finished eighth in the other TOM'S car, behind the Real Racing Honda of Koudai Tsukakoshi and Nobuharu Matsushita which had been in the podium fight but suffered a similar late drop-off in pace.
The Kondo Nissan that started on pole finally finished 10th behind the SARD Toyota, while the Rookie Racing car was out of the points in 11th.
GT300: Gainer Nissan wins with slick tyre gamble
The GT300 class, the #11 Gainer Nissan of Ishikawa and Tomita prevailed thanks to a well-timed switch to slick tyres in the closing stages.
It had been the polesitting Goodsmile Mercedes-AMG GT3 shared by Tatsuya Kataoka and Nobuteru Taniguchi that led the majority of the race, despite briefly dropping to third behind the #11 Nissan and the works Subaru BRZ in the wet opening stages.
After retaking the lead on lap seven, Kataoka maintained the lead through the first round of pitstops and stretched a gap of three seconds.
Taniguchi took over from Kataoka on lap 54 and led when the race was red-flagged, but on the restart he slipped back to third behind both of the Gainer Nissans, which excelled in the wet conditions.
As the track began to dry Taniguchi's Mercedes regained the initiative, moving back into the lead after an entertaining duel with Tomita.
After losing the lead, Tomita took the gamble of pitting for slicks on lap 81, and three laps later Taniguchi was also in the pits for dry tyres. But disaster hit the Goodsmile crew when Taniguchi suffered a spin at Turn 3 on his out lap.
With many other frontrunners pitting, it was the Subaru that retook the lead with Hideki Yamauchi attempting to make it to the finish on wet tyres, with the LM Corsa Toyota Supra of Hiroki Yoshimoto opting for a similar strategy.
However, Tomita was third and closing rapidly on wet tyres, closing down a gap of some 40 seconds in a matter of laps.
In the closing stages, Tomita passed both Yoshimoto and Yamauchi in quick succession to deliver Gainer its first win of the season.
The mixed conditions gave the Suzuka-winning Studie BMW M4 GT3 of Seiji Ara and Masataka Yanagida the chance to come through the field from 16th on the grid, and a well-timed final stop to slicks allowed Yanagida to finish second.
Ex-Formula 1 racer Roberto Merhi was third across the line in the Team LeMans Audi R8 LMS GT3 he shares with Yoshiaki Katayama, having also made an early call to take slicks.
Struggling badly in the closing laps, Yamauchi appeared to be on course for fourth before he was tipped into a spin by Yoshimoto exiting the final corner.
Yoshimoto was fourth ahead of the Kondo Racing Nissan of Joao Paulo de Oliveira and Teppei Natori, with the Subaru of Yamauchi and Takuto Iguchi slipping to seventh behind the apr Lexus LC500h that recovered from starting last following its exclusion from qualifying.
Taniguchi could only manage 12th at the chequered flag after his earlier off.
The LEON Racing Mercedes crew had to retire at two-thirds distance as Naoya Gamou had been forced to withdraw due to illness, leaving Takuro Shinohara to complete 66 laps solo before parking up.
GT500 results:
1. #3 Niterra MOTUL Z
2. #16 ARTA MUGEN NSX-GT
3. #100 STANLEY NSX-GT
4. #64 Modulo NSX-GT
5. #36 au TOM'S GR Supra
6. #38 ZENT CERUMO GR Supra
7. #17 Astemo NSX-GT
8. #37 Deloitte TOM'S GR Supra
9. #39 DENSO KOBELCO SARD GR Supra
10. #24 Realize Corporation ADVAN Z
11. #14 ENEOS X PRIME GR Supra
12. #19 WedsSport ADVAN GR Supra
13. #23 MOTUL AUTECH Z
14. #8 ARTA MUGEN NSX-GT
15. #1 MARELLI IMPUL Z
GT300 results:
1. #11 GAINER TANAX GT-R
2. #7 Studie BMW M4
3. #6 DOBOT Audi R8 LMS
4. #60 Syntium LMcorsa GR Supra GT
4. #56 Realize Nissan Mechanic Challenge GT-R
6. #31 apr LC500h GT
7. #61 SUBARU BRZ R＆D SPORT
8. #10 PONOS GAINER GT-R
9. #88 JLOC Lamborghini GT3
10. #52 Saitama Toyopet GB GR Supra GT
11. #2 muta Racing GR86 GT
12. #4 Goodsmile Hatsune Miku AMG
13. #30 apr GR86 GT
14. #360 RUNUP RIVAUX GT-R
15. #20 Shade Racing GR86 GT
16. #87 Bamboo Airways Lamborghini GT3
17. #18 UPGARAGE NSX GT3
18. #5 Mach Syaken Air Buster MC86
19. #50 ANEST IWATA Racing RC F GT3
20. #27 Yogibo NSX GT3
21. #48 Shokumou K's Frontier GT-R
22. #9 PACIFIC Vspo NAC AMG
23. #96 K-tunes RC F GT3
24. #22 R'Q's AMG GT3
25. #65 LEON PYRAMID AMG
26. #25 HOPPY Schatz GR Supra GT
27. #244 HACHI-ICHI GR Supra GT
