In the end, it was Sekiguchi that prevailed after putting up a stern defence on old tyres against Hirakawa, who was able to close in rapidly in the final few laps with his fresh Yokohama rubber.
Hirakawa came close to pulling off a move on the last lap at the downhill Turn 11 right-hander, the most obvious passing opportunity at a circuit where overtakes are notoriously few and far between, but Sekiguchi kept just close enough to the inside to force Hirakawa to go the long way round and hang on to the lead.
The battle - which came much to the delight of Impul boss Kazuyoshi Hoshino, who famously hates team orders - was only made possible thanks to Sekiguchi and Hirakawa opting for diametrically opposed strategies, giving the latter driver a 20-lap tyre offset.
Running sixth behind Hirakawa in the early stages, Sekiguchi dived for the pits as soon as the window opened on lap 10 of 37, which later proved to be a tactical masterstroke as the leading group hesitated to make their stops.
Sekiguchi himself admitted post-race that he felt the strategy was a mistake at first as he rapidly caught up with a train of three cars circulating at the rear of the field comprising Hiroki Otsu, Ritomo Miyata and Kazuya Oshima.
Race leader Toshiki Oyu at this point was lapping in the mid 1m36s, holding up Tomoki Nojiri, Sacha Fenestraz, Kenta Yamashita (who would soon drop out due to gearshift trouble) and Hirakawa. Once on fresh tyres, Sekiguchi was immediately into the 1m35s despite catching the slower cars of Oshima and Miyata, both of whom he had to pass on-track.
Once clear of that pair, Sekiguchi was only 28.8s down on race leader Oyu, who was still stuck in the mid-1m36s, and crucially with a clear track ahead thanks to Otsu pitting at the end of lap 13. Other drivers that could have gotten in the way like Naoki Yamamoto, Giuliano Alesi and Nobuharu Matsushita had already come in for their stops by this point.
Sekiguchi proceeded to post two laps in the low 1m34s range, so that the gap to the leader was down to 24.5s by the end of lap 15. With the pitlane time loss sitting around the 27-second mark, that was it. Sekiguchi was in the net lead.
Nojiri pitted at the end of lap 15, with Mugen focused only on getting their man out of the pits ahead of nearest title rival Fenestraz, and rejoined not only behind Sekiguchi but the Dandelion machine of Tadasuke Makino, who had run seventh before pitting on lap 11 (and would go on to finish third).
Oyu and Fenestraz pitted together next time by, giving Hirakawa clear air at the head of the field. Impul had effectively bought itself the victory by splitting its strategies, although this wasn’t the result of any grand team plan.
Kazuki Hoshino, son of Kazuyoshi and acting Impul team director, revealed post-race: “We didn’t decide on the strategy as a team, rather the respective crews of each car decided on the strategy they felt gave them the best chance and they just happened to be different.”
Regardless, Hirakawa did a superb job of nursing his Yokohamas until lap 30, never dropping out of the 1m35s range for the rest of his stint. His reward was an overcut on both Oyu and Fenestraz, and then his tyre offset meant he could make short work of both Nojiri and Makino to move into second.
Hirakawa disposed of Makino on lap 34 at Turn 5, giving himself three-and-a-half laps to catch and pass teammate Sekiguchi. There were no team orders, despite the fact that the extra five points for the win would have been a big help to Hirakawa’s now-fading title aspirations.
Sekiguchi was doing a solid job of looking after his tyres too though, and from lap 25 until the chequered flag he never dropped out of the 1m35s range. That meant that Hirakawa would be relying on outfoxing his teammate with the help of the Overtake System (OTS) to pass.
Asked by Motorsport.com about his showdown with Sekiguchi, Hirakawa said he felt he had lost the battle with a mistake using the OTS, falling into the trap of deploying it at the same time as his teammate with three laps remaining.
On that lap, Sekiguchi activated his OTS approaching the Turn 10 hairpin that leads on to the downhill straight before Turn 11, and Hirakawa did likewise. That meant both were unable to use the overtaking aid on the penultimate lap, as they were both amid their 100-second cool-off period.
“Sekiguchi used the button before the corner [Turn 10], so I should have not used it,” said Hirakawa. “That would have allowed me to use it on the next lap [while Sekiguchi was amid the cool-off period].
"If you push the button at the same time, you can’t pass even if you have fresh tyres. This was the biggest mistake. Even with the tyre mileage difference, it’s so difficult to overtake without the OTS."
While his tyres were past their best by now, Hirakawa still had the OTS advantage for the final lap because Sekiguchi used up the last 43 seconds of his 200-second allocation in the opening part of the final lap, while Hirakawa - who still had 56 seconds left to play with - was able to use up his remaining boost from the exit of Turn 4 all the way through to the end of the lap.
It was no use though, as Sekiguchi just barely held on during the final showdown at Turn 11, with Hirakawa going on the outside kerb and briefly catching air with his front wheels. “I wasn’t really close enough [to pass]," said Hirakawa. "But the key really was two laps before with the OTS, I wasn’t smart enough.”
Chasing a first win since 2019, Sekiguchi was in no mood to roll over. “I could see in my mirror that Hirakawa had passed Nojiri and Makino, so I knew he was coming fast,” he recalled. “He was getting closer and closer, but I was fired up to show my skills. I was determined to not leave the inside line open.
“I was thinking, better to go in too hot and run off-track than just leave the inside open and be passed easily. I made use of all my experience to hold him off.”
For Impul, there was no question of asking their drivers to hold station, but there were “mixed feelings” about one of them having to accept defeat.
“Hirakawa has suffered a lot in the last few races, and Sekiguchi dominated the last race at Fuji but couldn’t win because of something the team was responsible for,” Hoshino Jr said, referring to Sekiguchi losing a near-certain win with a loose wheel. “I wish that they could have crossed the finish line at the same time.
“With about three laps to go, I was next to the boss [Hoshino Sr] and I said, ‘I’m going to let them race’, and he shouted excitedly, ‘Let them race, let them race!’ I thought, ‘This is Team Impul’, and actually I got a little bit teary-eyed.”
Sekiguchi and Hirakawa delivered Impul a first one-two finish since way back in 2008, when Tsugio Matsuda led home Kohei Hirate at Suzuka. It was certainly fitting that the team’s 14-year wait was ended by a battle that captured the fighting spirit of Hoshino so well.
