Frances Tiafoe was well on his way to another early US Open exit.

The 22-year-old American had won the first set against John Millman in their second-round match Thursday, but midway through the second set, the Australian took over. Millman won seven straight games and 10 of 11, dominating the third set to take a commanding 2-1 lead

That’s when Tiafoe found a second level to ensure the longest stay of his career in Flushing.

With his back against the wall, Tiafoe turned on the afterburners and finished off a gutsy comeback win, 7-6, 3-6, 1-6, 6-3, 6-3. He advanced to the third round of the US Open for the first time in his career, after suffering first-round exits in 2015, 2016 and 2017, and bowing out in the second round in each of the past two years.

“It’s not about playing great tennis, it’s about competing your ass off and I think that goes a long way,” Tiafoe said. “You can win a lot of matches just putting it all on the line. That’s what I did today and I’m trying to strive to do more of that instead of just trying to always be on ESPN Top 10. Going to meat and potatoes and get busy.”

Despite often being tagged with the potential to be the next American men’s star, this marks just his third trip to the third round of a Grand Slam tournament in 17 career tries. Tiafoe previously reached the third round of Wimbledon in 2018 and the quarterfinals of the Australian Open in 2019.

In the pressurized fifth set, Tiafoe and Millman held serve before Tiafoe finally broke to take a 4-3 lead then broke Millman again at 5-3 to clinch the win.

“It’s kind of like, what’s the alternative?” Tiafoe said. “It’s COVID. You’re going to go back home, you’re going to be bored as hell. You can go crazy for an hour and a half, fourth and fifth set you can go dumb.”

Tiafoe, who withdrew from the All-American Team Cup in July after testing positive for COVID-19, was able to win Thursday despite his 73 unforced errors — 54 of them during the first three sets.

After receiving treatment on his right shoulder following the first-set tiebreaker, Tiafoe led 3-2 in the second set before Millman captured the next seven straight games to flip the momentum — only temporarily, as it turned out.

“I’ve lost some heartbreakers here at the Open,” Tiafoe said. “It was nice to get over the line here in New York.”