The 36-year-old Williams beat No. 24-seeded Anastasia Pavlyuchenkova 6-4, 7-6 (3) on Tuesday, becoming the oldest player to reach the Australian Open women's semifinals in the Open era.

Her 50th career win at Melbourne Park earned her a spot in the last four for the first time in 14 years.

"It's wonderful to start the year out with this appearance," said Williams, who hadn't reached the semifinals here since 2003, the year she lost the final to her sister, Serena. "I want to go further. I'm not happy just with this. But I'm so happy to be in the position to like go further."

She will next play either French Open champion Garbine Muguruza or CoCo Vandeweghe, who are both in the Australian Open quarterfinals for the first time.

"Whoever wins, I'm just so excited that I have an opportunity to play again," Williams said. "That's all I'm focused on."

Williams dropped four service games against Pavlyuchenkova, but she responded each time by breaking back. In the tiebreaker, she trailed 3-1 before winning the last six points clinching the match on Pavlyuchenkova's double-fault.

The seven-time major winner has advanced through the tournament without dropping a set, recovering from a right elbow injury that forced her to withdraw from a warmup tournament in New Zealand.

Now she is into semifinals for the second time in three majors after a six-year absence from the last four and for the 21st time overall.