Reigning series champion Yamashita was drafted in to join Hirakawa at the wheel of the #37 Toyota GR Supra for the final two races of the season, with Nick Cassidy ruled out of the title run-in due to his Formula E commitments.
The Motegi weekend got off to a difficult start on Saturday as Yamashita was tasked with navigating the first segment of qualifying and could only manage 13th on the grid.
But, taking the wheel for the opening stint of the race, the Toyota LMP1 protege rose to seventh before handing over to Hirakawa immediately after the safety car period.
Ryo Hirakawa, Kenta Yamashita, #37 KeePer TOM'S GR Supra
Ahead of the final race of the season at Fuji Speedway later this month, Hirakawa, is level on points with Real Racing Honda duo Bertrand Baguette and Koudai Tsukakoshi, albeit behind on countback with one win with to the #17 crew’s two.
Asked if he has any remaining concerns about racing alongside Yamashita in the title-decider, Hirakawa replied: “I just hope he can pass Q1 and I can try for pole position! But I think he should be fine for the race.”
Yamashita said he felt the fact he hadn’t driven a GT500 car since the opening round of the season at Fuji back in July played a role in his slow start to the weekend, but he was satisfied with his performance in the race.
“To be honest, until qualifying I was struggling a bit to drive, because I hadn’t driven a GT500 car for four months,” he told Motorsport.com.
“But in the race I think my driving was better and the car felt better. I had confidence, especially under braking, so I was able to overtake some cars.
“Considering we qualified in P13, I think P6 is ok. But everyone now has almost the same points, so it all depends on the final round. I think we have to win.”
#37 KeePer TOM'S GR Supra, #23 MOTUL AUTECH GT-R