The trajectory of an athlete's career is usually predictable. There is a beginning, a middle, an end. Those who trace a high-arcing parabola can call themselves dominant.
In tennis, among the most physically demanding of sports, that peak of powers typically lasts only a few years. In extraordinary cases, as with Roger Federer, it can be a sweet spot of six or seven years.
How, then, do you explain the phenomenon that is Serena Williams?
In 2002, Serena produced her finest season ever, winning three consecutive majors (beating sister Venus in all three finals) -- on the way to the Serena Slam that culminated with the 2004 Australian Open.
Sunday, a decade removed from that flourish -- after a series of peaks and valleys that will exhaust her biographers -- Williams completed the second-best year of her career. She defeated Maria Sharapova in the final at the TEB BNP Paribas WTA Championships 6-4, 6-3.
She did not drop a set in her five matches in Istanbul, Turkey. The last four points were all winners (sense a theme?) from Williams.
During one point in the first set, when she ran down a short ball, Serena -- almost skipping through the air -- could have been that 17-year-old who broke through at the U.S. Open 13 years ago.
"She's ranked ahead of me, so I felt like I had nothing I had to lose," Serena said afterward, revealing her ruthless, relentless mindset. "I feel great. You know, this is exactly my dream. I'm so happy I was able to achieve it."
In the end, Sharapova's fatal flaws in this awkward matchup (for her) against Williams -- a weak second serve and a chronic inability to cover the court -- did her in. Still, it was a moral victory of sorts, particularly after she was unhinged in the Olympic final 6-0, 6-1. Those seven games she took from Serena represented her best effort in years; Sharapova won a total of nine games in their previous three matches.
She did not even get a whiff of a break point, while Serena converted three of her six.
After losing a shocking first-round match to Virginie Razzano at Roland Garros, Serena finished the season in a blaze, winning 31 of 32 matches. She won the title at Wimbledon and the U.S. Open and the Olympic gold medal in singles and doubles, and now is the year-end champion for the third time in her career.
Not only did she become the oldest year-end champion ever at age 31 (Martina Navratilova was 30 when she lifted this trophy 26 years ago), but Serena was, far and away, the best player in women's tennis.
Don't let the rankings fool you; Victoria Azarenka is No. 1, followed by No. 2 Sharapova and Williams at No. 3. Serena, for the record, was 7-0 against them this year and won 14 of 15 sets.
More formidable facts from Serena, who:
• Finished the season winning 48 of 50 matches to finish with a record of 58-4 (.935) -- the second-best percentage in women's tennis since 1990.
• Earned her 12th consecutive victory against the No. 1- or No. 2-ranked opponent. The last such loss was more than five years ago -- in a meaningless quarterfinal.
• Has now gone a staggering eight years since losing to Sharapova, a string of nine straight wins.
Like her or not (the Williams sisters inspire a polarized following), Serena has always done it in her own, unique way. Over the years, she has been in and out of the game, mentally and physically, and it probably has helped to extend her longevity. Andre Agassi followed a similar course. Rafael Nadal, suddenly playing on merely mortal knees, might do well to take note.
Does this come close to her sensational 2002 season?
"Pretty much," Serena said, sounding uncertain in her on-the-court interview. "Yeah. It was a pretty slow start. I'm going to say 2002 was my best."
And then Serena smiled, and you could see her focus shift forward, to the Australian Open, which -- believe it or not -- convenes in less than three months.
"There's always 2013," she said. "I'm looking forward to it."
Consider yourself warned.