Kondo Racing driver Fenestraz went into Saturday's opening race of the Suzuka double-header facing a near-impossible task to overhaul the points advantage of Tomoki Nojiri, which grew to 35 points after qualifying.
While Nojiri claimed his second title with a relatively straightforward drive to second, Fenestraz made little progress from 17th on the grid and ended up in 16th in by far his least competitive showing of the season.
Looking back on his struggles, the Franco-Argentine driver said that the rebuild of his Kondo machine after his crash in Round 6 at Fuji, where he hit the barriers with force after contact with Naoki Yamamoto, created aero issues that hadn't been identified in the previous round at Motegi in August.
"It was definitely the worst day of the season," Fenestraz told Motorsport.com. "And to have that now when we are fighting for the championship, it's bad timing.
"We found some issues on the aero balance. It's the first time we came to a high-downforce track since the crash at Fuji, we have a fully new car and my engineer found some things after qualifying, like a weird aero balance.
"We had some tyre pressure issues in qualifying but then in the race we were just so slow, nearly a second a lap slower. We haven't been that slow all season. It was a long race, when you can see your position [on the timing tower] on the straight... it was a difficult one.
"Tomorrow we'll change a few things, but it's a shame. I really wanted to at least keep the championship going until tomorrow."
Fenestraz added that the very different nature of the Motegi track layout likely disguised the issues with the freshly rebuilt Kondo car.
"I was surprised how well it worked at Motegi [with the rebuilt car], but there are not many high-speed corners," he said. "When you arrive at this kind of track where the roll stiffness and the aero are really key, we found some odd things that were caused by the crash at Fuji.
"I don't know if it was the turning point of the championship, but if the crash didn't happen, I would have had more points and maybe I would have had a better day today.
"If I look back at the year there have been a lot of things that affected us, but now I can say the crash and having a whole new car really didn't help. At Motegi it didn't feel too bad, but here it was clear it didn't feel the same."
Hirakawa left to lament poor qualifying
As well as Fenestraz, Impul driver Ryo Hirakawa also saw his faint chances of overhauling Nojiri evaporate on Saturday, as he finished in ninth place from 11th on the grid.
Hirakawa failed to make up any places on the opening lap and spent a large chunk of the race stuck behind the slower Inging machine of Sena Sakaguchi as he opted for a strategy of leaving his pitstop until later in the race.
"We were not good in qualifying," said Hirakawa. "Q1 was ok but in Q2 we made a mistake on the set-up and we couldn't perform well. We qualified P11 which is pretty bad, because Suzuka is a hard track to pass.
"The start was not great, we couldn't go to the front, so the whole race was kind of staying behind a slow car, which was a shame. Once the other cars ahead pitted I had quite a good race pace."
Elaborating to Motorsport.com, he added: "It's easy to say now, but I was stuck behind Sakaguchi, he was in the 1m42s, but after he boxed I was able to do 1m41.0s without pushing too much, which means I at least had the pace to beat [Ren] Sato, who finished P3.
"But everything is because of the bad qualifying. I am sure that we are misunderstanding something. We have another chance to try tomorrow, but definitely something has been wrong which we're not sure about."
Fenestraz and Hirakawa go into Sunday's finale level in the fight for second in the points as they vie to finish the season as top Toyota driver.
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