She triumphed at Wimbledon, the Olympics and U.S. Open -- the three most important tournaments following the French Open -- and was barely troubled at the year-end championships in Turkey, despite almost two months of inactivity.
It's far from brave or adventurous to forecast that Williams won't be as untouchable in 2013. Winning all four majors is nearly impossible for a variety of reasons, as the record books tell us, and Williams hasn't bagged the French Open in more than 10 years.
Furthermore, closer inspection reveals Williams lapsed in the Wimbledon and U.S. Open finals, and instead of claiming majors No. 14 and 15, it could easily have been zero titles instead.
Victoria Azarenka served for the U.S. Open, you'll recall, and with another year under her belt, she will become a tougher opponent for Williams.
Having immersed herself in her tennis all of last year when she was determined to make a statement on court after a life-threatening illness, will Williams remain fully committed in 2013? She has been known to stray from tennis in the past.
We'll go for one or two majors for Williams -- which would be nothing to be embarrassed about.
2. Slam No. 2 for Petra
We will hear more from Petra Kvitova.
Remember Petra Kvitova, the tall, Czech lefty who won Wimbledon in 2011?
While Serena was doing her thing, Azarenka won her first major, Maria Sharapova completed her Grand Slam collection and Kim Clijsters retired, Kvitova was indeed the player women's tennis forgot in 2012.
By no means was it a poor year for Kvitova. She had success on North American hard courts for a change and reached the semifinals of the French Open. But Kvitova, who likes to maintain a low profile, no doubt had a tough time coping with her newfound fame.
More worrying was her health. Illness made for a fragmented season, and if her body continues to break down, Kvitova's great potential won't be fulfilled.
Thankfully, however, her issues were relatively minor.
Expect Kvitova to land her second Grand Slam title. She certainly won't be a one-Slam wonder.
When Wozniacki lost her No. 1 ranking and then slid outside the top five, cameras were nonetheless still close by, given the bubbly Dane's relationship with Rory McIlroy, the top-ranked golfer in the world. Be it tennis or golf, Wozniacki has a fondness for news conferences.
Wozniacki was defiant in Melbourne last year after relinquishing the top spot in the rankings, vowing that she'd return to No. 1: For one of the game's best competitors, the demotion stung.
For 2013, Wozniacki should be content with re-emerging in the top five.
By the end of 2012, Wozniacki focused more on making a charge in the rankings instead of dwelling on no longer being the No. 1: She won eight of her final nine matches.
Her first-round exit at the U.S. Open could be blamed on an injury, and Wozniacki held match points in a first-round loss at Wimbledon.
Don't get too carried away with Wozniacki and Kvitova's upset losses this week.
4. Robson into the top 15
Laura Robson had an impressive 2012.
It's not unusual to see players rise from outside the top 150 in the rankings to inside the top 60 in a season. More difficult is making the next jump, to inside the top 20 or 10. Angelique Kerber did it in 2012, becoming the leading member of the impressive German quintet.
Count on Britain's Laura Robson, a fellow lefty, to follow Kerber.
Robson, the former Wimbledon junior champion, finished 2012 at No. 53, a progression of 78 spots from 12 months earlier. The power baseliner's climb was based on winning matches at smaller tournaments (such as Guangzhou) but also, impressively, at majors, especially at the U.S. Open.
Her game and coach -- he divides opinions but Zeljko Krajan gets results -- mean Robson is looking good to feature in the top 15 and achieve a first Grand Slam quarterfinal. She'll outdo fellow Brit Heather Watson.
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There was a period recently when first-time winners were the norm at majors: Li Na, Kvitova, Samantha Stosur and Azarenka made it four straight from the middle of 2011 to last year's Australian Open. Sara Errani and Agnieszka Radwanska were first-time finalists in 2012.
But the chances of a first-time winner, or even finalist, in 2013 are small: Kerber is the likeliest candidate, yet her serve is exposed against the elite. Radwanska, meanwhile, won't repeat her 2012.
Williams' clash with Azarenka in New York was the women's match of the year in 2012, and pencil them in to battle in the Australian Open final if on opposite sides of the draw.