With Kamui Kobayashi having clashing FIA World Endurance Championship commitments at Spa, Lexus Team Sard was left searching for a replacement teammate for ex-Formula 1 driver Heikki Kovalainen.

It had the option of recalling the experienced Kohei Hirate, who was a part of 2016’s winning line-up alongside Kovalainen.

But it chose to put faith in Tsuboi, a Toyota youngster who has been steadily establishing a name for himself in his home country.

After winning the 2015 Japanese F4 title, Tsuboi enjoyed a successful maiden season in the Japanese F3 championship, finishing all but two races on the podium.

Although he missed out on the title a year later by just eight points, he recorded nine wins in the second half of the season, instantly grabbing the attention of his bosses.

He isn’t a stranger to GT cars either; a rookie GT300 campaign with LM Corsa yielded two wins and a third place in the championship.

As such, Tsuboi was perceived to be the perfect replacement for the highly-talented Kobayashi, and he did not disappoint.

Limited practice

Given the limited running he’s had in the Lexus LC500, Tsuboi would have hoped to do as many laps of the Fuji track in practice as possible. But heavy showers and fog severely disrupted the schedule, limiting him to just three laps before the race.

To compound matters, he had the added pressure of driving a race-leading car after Kovalainen vaulted from fifth to first in the opening stint.

But when several drivers struggled to get tyres up to temperatures in a series which doesn’t allow tyre warmers, Tsuboi perfected his outlap to maintain the lead of the race.

In fact, he went on to extend what was a two-second gap into a five-second lead before handing the car back to Kovalainen for the final stint.

Unfortunately, a dream debut win wasn’t to be as Nissan managed to leapfrog the Sard Lexus in the final round of pitstops, but a second place finish was still a remarkable result.

Tsuboi's faultless driver received plaudits from drivers up and down the pitlane, including his own teammate Kovalainen.

“Tsuboi-san did an amazing second stint. So strong with very little practice. He’s very talented, he’s very good,” Kovalainen told Motorsport.com.

“I expected exactly that. He can be very strong because in the testing so far, he hasn’t been testing much, but every time he’s been testing he’s been very strong, he is very confident, very focussed.

“He doesn’t make mistakes and he understands all the critical points. So I was not worried. He’s an excellent driver. He was able to maintain the gap and even sometime I open a little bit of gap.

“So he was really excellent and I think he’s going to be a very strong GT500 driver in the future, there’s no question about it.”

It remains to be seen what the future has in store for Tsuboi. After a breakthrough GT500 debut, the 22-year-old will return to the lower class of Super GT with Tsuchiya Engineering.

He scored a podium of the opening round of the season in Okayama and will be looking to carry on the good work in the next race at Suzuka.

Then there’s unfinished business in Japanese F3. While Tsuboi has proved himself more than enough in the FIA-sanctioned championship, he seems keen on grabbing the ultimate prize on his third attempt.

He’s already made a perfect start to the campaign, sweeping the season’s opening round at Suzuka. Could a title open the door to a 2019 Super Formula seat or a full-time GT500 drive? Only time will tell...

Additional reporting by Tomohiro Yoshita