Serena Williams defeats top-ranked Simona Halep to reach the quarterfinals at the Australian Open

Melbourne, Australia – Serena Williams survived a challenge from Simona Halep in the fourth round of the Australian Open, defeating the top-ranked player in the world 6-1, 4-6, 6-4.

Williams was pushed to a third set for the first time in the tournament, after a surge from Halep, who lost all of her service games in the first set, which lasted just 20 minutes.

"I felt like I'd been hit by a train," Halep said.

The French Open champion appeared to read Williams better in the second, improving the accuracy of her serves and becoming more aggressive, breaking the Williams at 5-4 to claim the second set.

She also had the 23-time Grand Slam champion on the ropes at 3-2 in that set, forcing Williams to save three breakpoints in a game that lasted 10 minutes before Williams held serve and leveled.

Williams broke again to pull ahead 5-3 in the third set, and held serve to claim the set and the match.

"I really needed to elevate my game, she's the No. 1 player in the world and there's a reason why," said Williams.

Collins, a two-time NCAA champion, was 0-5 in majors until this tournament. Barty is the first Australian woman in a decade to reach the quarterfinals at Melbourne. It's been 41 years since an Aussie won the women's title.

Williams will play No. 7 Karolina Pliskova, and No. 4 Naomi Osaka will meet No. 6 Elina Svitolina.

Osaka, the reigning U.S. Open champion, came from a set down in the fourth round to defeat Anastasija Sevastova 4-6, 6-3, 6-4.

No. 14 Stefanos Tsitsipas became the first men's player to reach the semifinals when he defeated No. 22 Roberto Bautista Agut 7-5, 4-6, 6-4, 7-6 (2).

Tsitsipas, who stunned Roger Federer in his previous match, is the first player from Greece to reach the last four at a major.

"I'm just living the dream," Tsitsipas said.

The other quarterfinals lined up like this: No. 2 Rafael Nadal vs. American Frances Tiafoe, No. 16 Milos Raonic vs. No. 28 Lucas Pouille and No. 1 Novak Djokovic vs. No. 8 Kei Nishikori.

Nadal hasn't dropped a set yet and hasn't lost to an American at a major since 2005.

Raonic defeated fourth-seeded Alexander Zverev in the fourth round in spectacular fashion 6-1, 6-1, 7-6 (7-5). Zverev committed 10 double faults and fired just six aces

Djokovic advanced with a 6-4, 6-7 (5-7), 6-2, 6-3 victory in three hours over Daniil Medevdev. "Definitely a physical battle," Djokovic said.