No woman since has even come close to that. But after winning Wimbledon and the U.S. Open last year, Williams appears to be poised for another dominant run, one that has her entertaining thoughts of a calendar year Grand Slam in 2013, starting with the Australian Open on Monday.
"I think for me, absolutely," Williams replied when asked if a Grand Slam is possible this year.
Williams cites one stinging loss in Paris as the motivation behind her recent string of success.
After a shocking upset loss to Virginie Razzano, then ranked No. 111, at the French Open last May—her only first-round defeat in a Grand Slam in 14 seasons on the tour—Williams rebounded to win titles at Wimbledon, the London Olympics, the U.S. Open and the season-ending WTA Championships.
She finished 2012 with a 58-4 record, losing only once after June, and with a title at the Brisbane International last week has extended her run to 35 wins in her last 36 matches.
In that time, she has beaten No. 1-ranked Victoria Azarenka four times, including at the U.S. Open final in which she saved two match points. She was 5-0 against Azarenka in 2012 and is 11-1 against her overall.
"Yeah, but I also lost in the first round of a Grand Slam and she didn't," Williams said. "I think that's what really affected me."
Azarenka is the defending Australian Open champion and Williams said the 23-year-old Belarusian deserves to have the top ranking because she was the most consistent player last year. Azarenka withdrew from their semifinal in Brisbane last week after having part of the nail on her big toe removed after a less-than-perfect pedicure.
No. 2-ranked Maria Sharapova was entered in the Brisbane International but withdrew with a sore right collarbone. Sharapova reached the final here last year, also after pulling out of the tuneup event in Brisbane, and then went on to win the French Open, her first major title in four years.
The pinnacle of Sharapova's 2012 season coincided with the lowest point for Williams, who followed her surprising fourth-round loss to Russia's Ekaterina Makarova at Melbourne Park with the loss to Razzano in Paris. That's when she went on the roll that has her confidently looking ahead to 2013.
"I think maybe whoever wins the Australian Open will have that same thought (about a calendar year Grand Slam)," she said. "There is no way that Victoria or Maria or maybe some other players don't feel the same way. So I think I definitely feel that way."
Sharapova has won each of the majors once, giving her a career Grand Slam spread across nine years. She thinks the depth in women's tennis makes it difficult for anyone to win them all in one season, but not impossible for somebody such as Williams.
"Well, she has the last two, so she's a couple steps closer than we are, that's for sure," she said. "Yeah, she had an incredible season. You know, the reason we still go out and play these matches is because we have to start from scratch and from the first round and from the first point. We have to do it again."
There's evidence of Williams' previous exploits all around Melbourne Park, from the entrance where spectators arriving on trains and trams have to pass her image five times just to get to the front gate, to the larger-than-life photo that the 15-time Grand Slam winner sees in the tunnel just before she walks onto center court.
She said it helps her feel at home.
"I love the crowd. I feel like if there is one tournament that everyone is rooting a lot for me is in Melbourne. I really don't get that everywhere I play," she said.
Williams can reclaim the No. 1 ranking by winning the Australian Open. If she does, she'd pass Chris Evert's mark of 30 years, 11 months and 3 days—set in 1985—as the oldest woman to hold the top ranking.
Evert, now a TV analyst, says it's "absolutely possible" for Williams to not only win in Australia, but to win all four majors this year if she stays fit and healthy.
"I think she's got the motivation, there's no doubt about it, because she's been out of the game so many different times, either for injuries or for other interests in her life, whatever, so she's still a fresh older player," Evert said.
"When she's on, she's unbeatable. I don't know if anybody can really stop her. But you have to remember that we're talking Grand Slams in the same sentence, and they're two-week tournaments and have always provided surprises for us.
"But is it possible? It's absolutely possible. Do I think it will happen? I have my doubts that it would happen only because she is human."
Williams thinks it's possible if she gets back into her zone, where "It feels really calm, like I'm in a really calm place and I'm not panicking, I'm not over-thinking it and not, you know, blasting every ball. I just get really calm and kind of serene.
"I feel better when I'm more calm. When I'm crazy like I was in Paris, as you can see, it doesn't do great for me."
She said she'd been spending a lot more time on court in practice, is more relaxed and "doing a lot of things I love," since hiring Paris-based Patrick Mouratoglou as a coaching consultant.
"Everything just came together with the right timing with me wanting to do better, with me wanting to work hard, him being there and having everything to work hard, and having the same mind frame of playing matches for the way I like to play.
"So I think life is about timing, and it was just good timing."
Williams joined other players from Mouratoglou's academy and former No. 1-ranked Martin Hingis on a trip to Mauritius, where the group mixed practice with singing karaoke and swimming in the sea.
Photos of Mouratoglou and Williams sparked rumors there was more to the relationship than tennis, something Williams declined to discuss when asked at a news conference if there was more to the story that she'd like to share.
"No, not really," she said. "Thanks for asking though."