Maria Sharapova reached a career milestone on Friday, which came as a nice surprise after a tough match.

"Oh, wow. I've won 600 matches?" Sharapova said, when an on-court interviewer congratulated her for the achievement earned by winning her third-round match Friday at the Australian Open.The No. 5-seeded player then thought a moment, and laughed nervously.

"Oh boy," she said. "Is this friendly reminder that I'm getting old?"

Sharapova is 28, which in tennis years means she's starting to wonder how much time is left in her career, and how much longer her body will allow her to compete in a sport filled with power-hitting youngsters.

The five-time Grand Slam winner hadn't dropped a set into the third round but struggled a bit before beating 22-year-old Lauren Davis 6-1, 6-7 (5), 6-1. After racing through the first set in just 26 minutes, Sharapova was broken twice in the second set, which lasted 77 minutes. She returned with more composure in the final set, making just five unforced errors and breaking Davis three times.

In the fourth round, Sharapova faces up-and-coming Swiss teen Belinda Bencic, who won her first two WTA titles in 2015 including at Toronto where she beat No. 1 Serena Williams in the semis followed by No. 2 Simona Halep in the final.

If anyone has proven that age is just a number it's Williams, who is 34 and has one of the greatest late career runs in sports history. She has won 21 Grand Slam titles, including six Australian Opens, and is still going strong.

Sharapova could face Williams in the quarterfinals, which would be the latest in their long-running rivalry. Sharpova hasn't beaten Williams since 2004, losing their last 17 meetings including last year's Australian Open final.

But after Friday's milestone, Sharapova took a moment to pause and reflect on her 600 career wins.

"I think it's a proud number," she said at her post-match news conference. "I've been doing it a long time. That's a fact."

Sharapova was 9 when she moved from Russia to Florida with her father, Yuri, to train at the famed Nick Bollettieri tennis academy. Three years earlier, when she was 6, Sharapova was spotted at a Moscow exhibition by Martina Navratilova, who told her father that America was the best place to cultivate the young player's talent.

It meant a two-year separation from her mother, Yelena, who stayed in Russia because of financial reasons and the wait to obtain a visa.

Asked Friday how she navigated the world of professional tennis as a young player, Sharapova credited her parents.

"You know, my father paved this career for me, that I just keep following," she said. "He just really opened the door to my dream. I'm just kind of living it."

"My mother opened up the world to me culturally, educationally. So I got very different things from both of them," Sharapova said.

When she was younger, Sharapova never would have imagined she would still be playing tennis now. But age and experience — and the injuries that have derailed her career at times — have made her realize what she appreciates.

"I really love what I do. Although I'd love to sit on the beach and read a book and drink margaritas, after a few days I get bored," Sharapova said. "At 28 years old, I'm healthy and look forward to playing for many years."