MELBOURNE, Australia (AP) — Frances Tiafoe had never played a No. 1, had never beaten anyone in the Top 5, and now he'd just won a tiebreaker against Novak Djokovic to level their second-round match at the Australian Open.

He nodded, soaked up the applause, skipped around the court motioning for more noise before plonking down in his courtside chair and saying what everyone watching already knew: “I love this. ... I love it!”

Tiafoe, a 23-year-old American who reached the quarterfinals here two years ago, threw everything he could at eight-time Australian Open champion Djokovic. He pulled the crowd into the contest, too. But it wasn't quite enough, with the defending champion winning 6-3, 6-7 (3), 7-6 (2), 6-3 in a 3 1/2-hour afternoon match on Rod Laver Arena.

“He pushed me to the very limit," Djokovic said. “I was trying to work around his backhand and kind of penetrate through the court there, open him up, but he wasn’t giving me anything.

“He’s a very quick player. It’s unpredictable what comes next ... I’m really glad to overcome such a battle."

The fourth set was on serve and appeared headed for another tiebreaker when Tiafoe was given a time violation on his serve. He lost his temper, and his serve. He didn’t win another game in the match, which finished with a double-fault.

Tiafoe shook his head, then jogged to the net to embrace Djokovic. He’ll take plenty from this.

Djokovic bowed, touched the court with his hand, and then went into his more customary celebrations at a court where he's won the title eight times and feels right at home.

“Credit to him for forcing me to feel uncomfortable," Djokovic said.

Djokovic served 26 aces, Tiafoe 23. Djokovic had the edge in terms of winners (56-49) and converted five of his break-point chances, while Tiafoe converted two of his three.

After taking a quick look at the stats, Djokovic said he couldn't remember serving more aces, or seeing more serves pass him, in a match in a long time. He'll next play No. 27-seeded Taylor Fritz, who held off Reilly Opelka 4-6, 7-6 (6), 6-7 (4), 7-6 (5), 6-2.

Stan Wawrinka, the 2014 Australian Open champion, wasted a big lead in the fifth-set tiebreaker — and three match points — before succumbing 7-5, 6-1, 4-6, 2-6, 7-6 (9) to Marton Fucsovics.

Dominic Thiem, who lost the final last year to Djokovic but went one better to win the U.S. Open, took a short route to the third round with a 6-4, 6-0, 6-2 win over Donimik Koepfer.

So did another U.S. Open champion, Naomi Osaka, who needed only an hour to sweep Caroline Garcia 6-2, 6-3.

Serena Williams kept her bid for a 24th Grand Slam singles title on track, making only 11 unforced errors as she defeated Nina Stojanovic 6-3, 6-0.

But a 21st trip to Melbourne Park ended painfully for her older sister, Venus Williams.

The seven-time major champion was trailing 1-5 in the opening set against Sara Errani when she landed awkwardly on her ankle as she approached the net for a volley. She fought back tears before receiving treatment on the ankle, and gamely continued, hobbling between points, before losing 6-1, 6-0.

The 40-year-old Williams was making her 88th Grand Slam main draw appearance, the most among women in the Open era.

Former U.S. Open champion Bianca Andreescu, coming back from 15 months out with injury, became the latest top-10 player to be beaten by Hsieh Su-wei of Taiwan. The eighth-seeded Andreescu’s power was no match for Hsieh’s shot-making in a second-round upset, 6-3, 6-2.

The 20-year-old Canadian seemed befuddled by the 35-year-old Hsieh’s unorthodox game, which includes a two-handed forehand and an unpredictable mix of pace and placement.

Hsieh is ranked 71st and has a history of inconsistency. But she’s 8-2 against top 10 players, including two wins over a reigning No. 1.

“It’s strange. I normally feel more excited to play with better players,” Hsieh said.

French Open champion Iga Swiatek beat Camila Giorgi 6-2, 6-4 and advanced along with No. 7-seeded Aryna Sabalenka and Ann Li, a 20-year-old American who beat Alize Cornet 6-2, 7-6 (6).

Two-time Wimbledon champion Petra Kvitova, the 2019 Australian Open runner-up, lost to Sorana Cirstea 6-4, 1-6, 6-1. Garbiñe Muguruza, the Australian Open runner-up last year, defeated Liudmila Samsonova 6-3, 6-1.

In men’s play, No. 11 Denis Shapovalov beat Australian qualifier Bernard Tomic 6-1, 6-3, 6-2, advancing along with two other Canadians, Milos Raonic and Felix Auger-Aliassime.

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AP Sports Writer Steven Wine in Miami contributed to this report.

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