MELBOURNE — Frances Tiafoe rolled up his white shirt’s right sleeve, flexed his biceps and slapped the muscle five times. Then he pounded his chest and yelled, ‘‘Yeah! Let’s go! Let’s go! Come on!’’
Forgive the young American’s exuberance. This was, after all, the biggest victory of his nascent career.
Down a set and 3-0 in the second, the 20-year-old Tiafoe came back to stun two-time Grand Slam finalist and No. 5 seed Kevin Anderson of South Africa, 4-6, 6-4, 6-4, 7-5, on Wednesday in the Australian Open’s second round.
‘‘I went to a different place. I dug insanely deep,’’ the 39th-ranked Tiafoe said. ‘‘It’s all about competing. Guys are so good. It’s just about how badly you want it. I want it real bad.’’
He was joined in the third round by another kid from the US who’d never been that far at Melbourne Park, 21-year-old Taylor Fritz, who saved 12 of the 13 break points he faced while dispatching No. 30 seed Gael Monfils of France, 6-3, 6-7 (8), 7-6 (6), 7-6 (5).
Next for Fritz is a matchup against Roger Federer, the two-time defending champion in Australia and owner of 20 Grand Slam titles.
‘‘I grew up watching a lot of the guys I play today. I can’t tell you how many times I watched Monfils’s highlight reel on YouTube, just growing up. ‘Fed,’ obviously, my whole life growing up, he was always the best, winning everything,’’ Fritz said. ‘‘So it’s really cool being able to step on the court with him again.’’
A day after American men went 1-5, the country’s contingent produced those two upsets and threw a couple of scares into other seeded players, too, but couldn’t pull off the wins.
Mackenzie McDonald pushed No. 6 Marin Cilic before losing, 7-5, 6-7 (9), 6-4, 6-4, and Denis Kudla went to a fifth set before bowing out, 6-4, 7-5, 3-6, 6-7 (6), 6-4, against No. 18 Diego Schwartzman. Reilly Opelka, a 21-year-old who eliminated No. 9 John Isner in an all-US first-round showdown, held a 67-2 ace advantage — and a 15-inch height advantage — against Thomas Fabbiano but lost to the Italian, 6-7 (15), 6-2, 6-4, 3-6, 7-6 (5).
‘‘This group [of Americans] really deserves the hype, I guess, because I think everyone’s good,’’ Fritz said.
Cilic was the 2014 US Open champion and the runner-up at Melbourne Park to Federer last year. Against McDonald, an NCAA champion in singles and doubles at UCLA who is 23 years old and ranked 81st, Cilic delivered 25 aces, including on each of the last two points.
‘‘It was a much tougher match than I expected,’’ Cilic said. ‘‘I didn’t know much about him.’’
For Tiafoe, it helped that Anderson’s best attribute, his intimidating serve, slowed down along the way because of problems with his right arm. Anderson was repeatedly visited by a trainer during changeovers and he lost pace on his first serves as the match wore on.
Anderson was the runner-up at Wimbledon last year and at the US Open in 2017 and had won all three previous matchups against Tiafoe.
But Tiafoe ended a six-match losing streak against top-10 opponents and is into the third round at a major for the second time, equaling his best showing.
Federer, seeking a record seventh Australian Open title and third in a row, beat Dan Evans, 7-6 (5), 7-6 (3), 6-3, and 2009 champion Rafael Nadal set up a third-round showdown against 19-year-old Australian Alex de Minaur with a straight-set victory of his own.
The defending women’s champion, Caroline Wozniacki, also advanced in straight sets, beating Johanna Larsson, 6-1, 6-3, and will face Maria Sharapova next.
In early Wednesday night action, sixth-seeded Elina Svitolina kicked off proceedings at Rod Laver Arena with a 6-4, 6-1 second-round win over Viktoria Kuzmova.
Svitolina will next play either Karolina Pliskova or Madison Brengle.
Wang Qiang and Camila Giorgi made short work of their second-round opponents at Melbourne Park, sweeping to straight-set victories.
Wang, the 21st-seeded player, beat Aleksandra Krunic, 6-2, 6-3, in 58 minutes. No. 27 Giorgi needed just a minute longer to defeat Polish qualifier Iga Swiatek, 6-2, 6-0.