Hirakawa, the 2017 SUPER GT champion and 2020 Super Formula runner-up, was drafted in to Toyota's full-season WEC line-up for the 2022 season in place of the retiring Kazuki Nakajima.
But the Japanese driver's relative lack of experience didn't show as he didn't put a wheel wrong during his stints aboard the #8 Toyota GR010 Hybrid that eventually beat the sister #7 car by a little over two minutes.
Hartley described Hirakawa as a "great addition" to the #8 crew after taking the chequered flag to seal the victory, saying his new teammate did an "awesome" job in his third Le Mans start, his first since 2017 and first in the top class.
Hirakawa said post-race: "I still cannot believe it. This is not my first time [sharing with Buemi and Hartley], we’ve done many tests and two races [at Sebring and Spa], but the teamwork is very nice.
"Since the test day we have been doing good steps, we all made no mistakes and did a good job."
Asked whether he felt pressure as the rookie in the Toyota line-up, Hirakawa replied: "Actually a lot, yes. I couldn’t sleep for a week. I haven’t slept properly. It’s a kind of pressure I never felt.
"Also yesterday to today [Sunday], I didn’t sleep. Maybe it’s a bit the adrenaline but it’s also the pressure, I guess. I hope I can sleep well tonight!
"They have a lot of experience and they are of course fast, so to catch up with them, you have to be very good. Also to fight against car #7 all race… it was hard, but in the end we did it."
Hirakawa's Le Mans victory came almost a year to the day since his first test of the GR010 Hybrid at Portimao.
"It was exactly one year ago in June," he reflected. "I was really bad when I first drove this car. It’s a heavy car and everything was new for me. I was really struggling.
"I didn’t expect to win Le Mans after one year like this. But not only me, all the team helped me since the announcement [that Hirakawa would replace Nakajima last winter], and now we’ve done it."
Hirakawa becomes the fifth Japanese driver to win Le Mans outright after Masanori Sekiya, Seiji Ara, Nakajima and Kamui Kobayashi, as well as the youngest at the age of 28.
"I don’t feel I’m a young man!" he jested. "But now I try to win as many as possible. That’s my next dream."
