The third set took 2:22 and momentum swung. Halep wasted chances to serve for the match in the ninth, 11th and 15th games, then had to save three match points in the 22nd. There were 11 service breaks and two medical timeouts — for Davis to get treatment on both feet — before Halep converted on her first match point.

"I never played the third set so long, so I'm really happy I could stay and win it. I'm almost dead," Halep said of the match which equaled Chanda Rubin's win over Arantxa Shanchez Vicario in 1996 — also 48 games — for the Australian Open record in terms of most games.

"I just feel that my muscles are gone," said Halep, who badly twisted her left ankle in the first round. "My ankle is, I don't know how it is because I don't feel it anymore!"Halep will play Naomi Osaka, who beat 18th-seeded Ash Barty 6-4, 6-2. No. 20 Barbora Strycova beat U.S. qualifier Bernarda Pera 6-2, 6-2, leaving U.S. Open finalist Madison Keys as the only American woman to reach the fourth round.

Keys advanced 6-3, 6-4 over Ana Bogdan and will next play No. 8 Caroline Garcia, who beat Aliaksandra Sasnovich 6-3, 5-7, 6-2. Sixth-seeded Karolina Pliskova beat No. 29 Lucie Safarova 7-6 (6), 7-5.

In the last night match, Hsieh Su-wei followed up her win over Wimbledon champion Garbine Muguruza by beating No. 26 Agnieszka Radwanska 6-2, 7-5 to return to the fourth round at Melbourne Park for the first time in a decade. Her assignment will get tougher, with Kerber up next.

Six-time Australian Open champion Djokovic continued his comeback from six months out with an injured right elbow, beating No. 21 Albert Ramos-Vinolas 6-2, 6-3, 6-3.

"I obviously have to be more humble this time with my expectations because I haven't played for six months," the 14th-seeded Djokovic said.

Federer entered the Australian Open last year under similar circumstances, coming off an extended break for a knee injury, and went on to win the title. His defense moved through another round with a 6-2, 7-5, 6-4 win over No. 29 Richard Gasquet.

Second-seeded Federer's next opponent is former world junior No. 1 Marton Fucsovics, who beat Nicolas Kicker in straight sets.

Djokovic will next face Hyeon Chung, who took out a Zverev for the second time this week. Chung beat fourth-seeded Alexander Zverev 5-7, 7-6 (3), 2-6, 6-3, 6-0 six days after a win over No. 32 Mischa Zverev in the first round.

Another unexpected loss at a major had the highly-touted Zverev admitted he may have a problem.

"Definitely not physical, so... I have some figuring out to do, what happens to me in deciding moments in Grand Slam," he said.

The 20-year-old Zverev has five titles on the elite tour but his fourth-round exit at Wimbledon last year remains his best run at a major.

Tomas Berdych ended 2009 U.S. Open champion Juan Martin del Potro's return to Melbourne Park for the first time since 2014 with a 6-3, 6-3, 6-2 win.

Fifth-seeded Dominic Thiem beat Adrian Mannarino 6-4, 6-2, 7-5 to set up a fourth-round match against Tennys Sandgren, who continued his career-best run by beating Maximilian Marterer 5-7, 6-3, 7-5, 7-6 (5).

AP