ISTANBUL, Turkey—The night before the final of the WTA Championships, a drained Serena Williams mentioned how she finally knew what it was like to hit the wall. Somehow, with an assist from her semifinal opponent, the exhausted American had managed to scratch out a win over Jelena Jankovic, but Li Na was in substantially better form than the Serbian, and it would be a much larger task for Serena to repeat the feat over the soon-to-be world No. 3 today.

Li has been working hard for about a year at installing serve-and-volley as part of her overall attack, but even though she does this in constantly in practice, in matches she's only comfortable using it as an occasional diversion of style.

On the first point of her opening service game, Li successfully served-and-volleyed, grabbing the point with a sweet backhand volley winner. Her willingness to employ the tactic proved critical in the first set, but her sporadic serve, as well as her fragile mentality, would eventually contribute to her undoing in Williams' 2-6, 6-3, 6-0 victory.

Li broke Williams to 2-1 by wrong-footing her with a cross-court backhand, and held to 3-1 with a half-volley winner. Like she did against Jankovic in the second set on Saturday, Serena was pushing her serve and groundstrokes and didn't seem willing to run.

Li, who owns one of the game’s most powerful and accurate two-handers, held to 5-1 with a running backhand pass cross-court. Serena uttered her first (positive) grunt while holding to 5-2, a signal that she was not dead yet, but Li ended the set the same way she had started it: Attacking the cords behind a solid serve.

Serena began the second set with much more energy, imploring herself to at least stay competitive. Gradually, as her fight returned, so did her power and movement. She broke for a 2-0 lead when her foe muffed a low volley, and although Li broke her back in the fifth game, Williams had begun to dictate play and was poking into her opponent's more vulnerable forehand side. Serena broke a sloppy Li at love to go up 5-3, fought off two break points, and then saw Li frame a forehand. After winning the final three games of the second set, Williams and Li were on to a deciding third.

Outside of her outstanding and somewhat improbable run to the 2011 Roland Garros title, Li’s career has been a series of almosts when it comes to grabbing big titles. Once again, her confidence quickly began to sink at a critical juncture, and she again looked like the same shell of player whom Serena had smoked in this year's U.S. Open semis.

Li double faulted to open the set and was then broken again to fall behind 0-3 when she charged the net and Serena passed her with a hard backhand swing volley. It looked as if Li no longer felt like she belonged on the same court with the 17-time Grand Slam champion.

Li confirmed that suspicion as the set quickly progressed. She doubled faulted for the 10th time to be broken for the third time in the set, and stood by while Serena won her fourth WTA Championships title with a bagel set and two nuclear, down-the-line backhands. Williams ends her season with a career high 11 titles, a 78-4 record, and at the not-so-tender age of 32, as the dominant player in her sport.

In her current form, Serena could very well pass Chris Evert and Martina Navratilova for overall Slam titles in  2014 (they have 18 apiece), and may even catch the legendary Steffi Graf (22) before her career is over. For a girl who grew up on the other side of the freeway in Compton, CA, that’s some pretty heady stuff.