MELBOURNE, Australia -- 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 4-6, 6-4, 6-4, 7-5 on Tuesday in the Australian Open's second round.
"I went to a different place. I dug insanely deep," the 39th-ranked Tiafoe said during an on-court interview. "It's all about competing. Guys are so good. It's just about how badly you want it. I want it real bad."
It helped that Anderson's best attribute, his intimidating serve, slowed down along the way because of problems with his right arm. The South African was repeatedly visited by a trainer during changeovers, and he lost about 5 mph 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 he had won all three previous matchups against Tiafoe.
But Tiafoe ended a six-match losing streak against top-10 opponents and is now into the third round at a major for the second time, equaling his best showing.
It he defeats Andreas Seppi of Italy next, Tiafoe would make his debut in the second week of a Grand Slam.
"If I'm playing on that day and beat somebody, that's the best present I can get," said Tiafoe, who will turn 21 on Sunday.
Another 20-something from the U.S. threw a scare into another older, more-accomplished top-10 foe, but Mackenzie McDonald couldn't match Tiafoe's upset, losing to No. 6 Marin Cilic 7-5, 6-7 (9), 6-4, 6-4.
Cilic was the 2014 US Open champion and the runner-up at Melbourne Park to Roger 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.
Seeking a record seventh Australian Open title and third in a row, Federer continued his strong run against qualifiers at Grand Slam tournaments with a 7-6 (5), 7-6 (3), 6-3 win over Daniel Evans.
Federer also maintained his 100 percent record of reaching the third round at the Australian Open -- 20 times in a row.
He has lost just once in 27 matches against qualifiers in majors, and that came to Mario Ancic at Wimbledon 17 years ago.
After two tougher-than-expected sets, Federer broke Evans' serve to take a 3-1 lead in the third set and served out the match.
"I couldn't pull away early in the match," said Federer, who actually was two points from dropping the opening set.
American Taylor Fritz outlasted 30th-seeded Gael Monfils in a 3-hour, 24-minute second-round match and will play Federer in the next round. Fritz prevailed 6-3, 6-7 (8), 7-6 (6), 7-6 (5), closing with his 15th ace of the match.
"I grew up watching a lot of the guys I play today. I can't tell you how many times I watched Monfils' 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."
Rafael Nadal, the 2009 Australian Open champion, set up a third-round showdown against 19-year-old Australian Alex de Minaur with a 6-3, 6-2, 6-2 victory over Matthew Ebden.
Reilly Opelka's 67 aces and 97 winners weren't enough to overpower diminutive Italian Thomas Fabbiano, who won 6-7 (15), 6-2, 6-4, 3-6, 7-6 (5) to reach the third round for only the third time at a major.
Other seeded men advancing Wednesday included No. 14 Stefanos Tsitsipas, No. 18 Diego Schwartzman and No. 26 Fernando Verdasco.
In men's doubles, the Bryan brothers opened with a 7-6 (4), 7-6 (1) win over Alex Bolt and Marc Polmans.
Bob Bryan was sidelined last year after injuring his hip in the lead-up to the French Open, and Mike paired with fellow American Jack Sock to win the Wimbledon and US Open titles and the ATP Finals, taking the world No. 1 ranking on his own.
With Bob back to full fitness, the 40-year-old twins returned for the ASB Classic in Auckland earlier this month and reached the semifinals before heading to Melbourne for the Australian Open.
The Bryan brothers, who have won 16 Grand Slam doubles titles together, will meet Adrian Mannarino and Andreas Mies in the second round at Melbourne Park.
The Associated Press contributed to this report.