MELBOURNE, Australia (AP) — 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. Anderson was repeatedly visited by a trainer during changeovers and he lost about 5 mph (10 kph) on his first serves as the match wore on.

Anderson was the runner-up at Wimbledon last year and at the U.S. 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 now into the third round at a major for the second time, equaling his best showing.

Defeat Andreas Seppi of Italy next, and Tiafoe would make his debut in the second week of a Grand Slam.

He turns 21 on Monday and said: “If I’m playing on that day and beat somebody, that’s the best present I can get.”

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 U.S. 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.

Federer, seeking a record seventh Australian Open title and third in a row, reached the third round by beating Dan Evans 7-6 (5), 7-6 (3), 6-3.

“I couldn’t pull away early in the match,” said Federer, who actually was two points from dropping the opening set.

The defending women’s champion, Caroline Wozniacki, was in action later Wednesday, along with Rafael Nadal, Maria Sharapova and Angelique Kerber, all of whom have won the Australian Open.

Other seeded men advancing in the afternoon included No. 14 Stefanos Tsitsipas and No. 18 Diego Schwartzman, who edged Denis Kudla of the U.S. 6-4, 7-5, 3-6, 6-7 (6), 6-4, and No. 26 Fernando Verdasco.

Three seeded women were sent home, including No. 24 Lesia Tsurenko of Ukraine, a 6-0, 6-2 loser against 17-year-old American Amanda Anisimova. No. 9 Kiki Bertens and No. 20 Anett Kontaveit also exited.

No. 5 Sloane Stephens opened the day in Rod Laver Arena with a 6-3, 6-1 victory over her junior doubles partner Timea Babos.

Stephens, the 2017 U.S. Open champion and a semifinalist here in 2013, reached the third round of the Australian Open for the first time since 2014.

“I’m kind of conquering all the places where I’ve been terrible,” Stephens said.

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