Will Serena Williams ever slow down?

There are four women in Melbourne -- Caroline Wozniacki, Petra Kvitova, Victoria Azarenka and Maria Sharapova -- with a chance to emerge next Saturday as the No. 1-ranked player in the world.

Ask Serena Williams if she cares.

She was No. 1 five times, spanning nearly nine years, for a total of 123 weeks. At 30 years old, she has won 13 Grand Slam singles titles and now -- with her 6-1, 6-1, third-round win over Greta Arn Saturday night -- 211 major victories, the most of her generation.

One record Serena does not have is most match wins among active players; that belongs to older sister Venus, with 598. Serena hit No. 500 when she defeated Barbora Zahlavova Strycova in the second round.

"Really, really cool," Serena said. "The first thing I asked, of course, is there anyone that achieved a thousand? I guess not. I never will get there, either."

Is Venus the next target?

"My target is just to keep going," Serena said. "I don't know what the next milestone is. I don't know."

This is what Serena does: just keep going.

Former rival Justine Henin, a seven-time Grand Slam singles champion who retired twice (in 2008 and 2011) is a year younger. Martina Hingis, a five-time major champion, is only a year older than Serena -- and she retired more than four years ago. Kim Clijsters (four major titles) says she will retire for the second and last time at the end of the season. She'll be 29.

Hard as it is to believe, this is Serena's 16th WTA season. For more than half her life, she has been a tennis professional. Of course, it sometimes gets old.

"I don't love tennis today," she said recently, sparking headlines around the world, "but I'm here and can't live without it."

Nor we tennis fans, if the truth be told, without her. Whether you like her or not -- and many don't -- she is undeniably, consistently compelling. Even haters will miss her when she steps away for the final time.

Serena has yet to officially retire, but she has effectively left the circuit three times, which makes it almost feel that way. She missed eight months with a left knee injury in 2003-04 then, three years later, another six months with the same malady. Last year, in the wake of a series of horrific health scares, she returned after an 11-month absence.

She has made a fine living coming out of the weeds. Clearly, she has grown accustomed to the rhymes and rhythms of these comebacks. One suspects she has even grown to embrace these peaks and valleys. Consider this: She has failed to play at least one major tournament in nine seasons; by contrast, Roger Federer -- whose 16 majors are the men's standard -- has gone more than a dozen years without missing even one.

In the 13 years since she broke through with her first major, the 1999 U.S. Open, Serena has averaged exactly one Slam victory each year. Is there any reason to think she won't keep that streak going in 2012?

Arn, certainly is a fan. The 32-year-old Hungarian -- she and Serena were the oldest women left in the draw -- called Serena "the real No. 1" before they met and said playing her was "an absolute privilege."

Oddly enough, this was their first meeting. It did not go well for Arn, who won only 31 of 90 points. Serena, challenged in her last service game, came up with two of her three aces in the match and went on to win in 59 minutes.

Despite the score, she was not overly impressive -- or impressed with herself. The ankle injury she suffered in Brisbane, she said, is coming around.

"I'm still working myself into the tournament," Serena said afterward. "It's [the ankle] definitely a lot better. So much treatment, every day. More than my match -- upper-intense."

Serena caught a break early Saturday, when unseeded Ekaterina Makarova upset No. 7 seed Vera Zvonareva, 7-6 (7), 6-1. They'll meet in the fourth round with a possible quarterfinal match against Sharapova looming in the quarters. Serena now has a 17-match win streak going in Melbourne. She won back-to-back titles in 2009-10 before missing the event in 2011. Her last loss in the Australian Open was in the 2008 quarterfinals to Jelena Jankovic.

"I'm just not striking the ball as well as I'd like," Serena said. "I need to relax and go for it."

Greg Garber is a senior writer for ESPN.com.