Oyu, who has joined the rebranded Servus Japan-run TGM outfit for 2023 after three seasons at Nakajima Racing, qualified third for the second round of the season, and passed poleman Nojiri on the opening lap into Turn 3.
He maintained the advantage until the safety car was called shortly before the pit window opened on lap 10 of 41, which prompted almost the entire field to come in for their mandatory tyre changes under caution.
Oyu was jumped by Mugen driver Nojiri in the pits, but when the race resumed on lap 13, Oyu launched an attack on the two-time champion heading down to Turn 1, only to lock up and flatspot his tyres.
That was the start of a descent down the order for Oyu, who was down to sixth place and struggling for pace by the time he bailed out and pitted for a second time, condemning him to a 20th-place finish.
"I was slow on the straights," Oyu told Motorsport.com's Japanese edition. "The timing of the safety car wasn’t good and Nojiri passed me in the pits.
"At the time, I didn’t think I was going to get another chance, I thought he would just pull away. But I got a good restart when the safety car came in and I decided to challenge him.
"We were both using the OTS, but when I pulled out of the slipstream, I dropped back a bit, and I had no choice but to brake as late as possible.
"Normally when you are in the slipstream that long, you should be able to at least get your nose in front. But we couldn’t, so our straight line speed must be bad.
"The flat spot was not that bad, but I originally had a feeling that the front [grip] would get tougher in terms of set-up as the race went on, so that just exacerbated the problem, and I lost pace."
Despite the disappointment of losing a chance to fight for a podium finish, Oyu said he was satisfied with the potential he and TGM had been able to demonstrate over the course of the Fuji weekend.
"On the plus side, I was able to set the fastest lap, and my battling at the top I was able to show my strength and that of the team," said Oyu.
"So if we can improve even more from now on, I think we'll be able to be on pole and win races this season."
Bolukbasi delighted with first Super Formula points
In the opening race at Fuji, Oyu led home team-mate Cem Bolukbasi, who managed to bag four points on his Super Formula debut in eighth.
The Turkish driver, who contested a part-season in Formula 2 last year, made his way up from 20th on the grid with a clean run as many other drivers ran into trouble with contact and penalties.
"It wasn't that much of a surprise, because I knew from qualifying the car was good," Bolukbasi told Motorsport.com.
"The start was very good and the timing of the safety car helped us. I just kept it consistent and clean, managed to overtake a few cars.
"I'm happy because it's been quite a while since I finished in the points. It's good motivation for myself and the team, because I expected the progress to be a bit slower.
"I've been enjoying working with the team, on and off the track, helping me to feel at home here. I think we can build from here."
Bolukbasi was a more subdued 17th on Sunday, reporting struggles with understeer after overnight adjustments and gearbox issues.
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