Who is the best female tennis player in the world? For the last three years, injuries and inconsistency have made that question impossible to answer with certainty. As the year-ending WTA Championships begin this week in Madrid, however, things are about to change. The future — and here we must insert a warning to fans of Justine Henin-Hardenne or Amelie Mauresmo about the disturbing, some might even say obscene, language to follow — belongs to Maria Sharapova.

We all knew the 19-year-old Russian could strike a mean ball, but her limited variety and cement shoes were liabilities on every surface. Those flaws are not as noticeable these days. Since her comprehensive (frankly, easy) victory in the U.S. Open final, Sharapova hasn’t let up, winning two titles. She is undefeated in her last 16 matches, not counting a withdrawal in Moscow after she won her first round.

Nothing magical has happened to Sharapova. She was already on par with women like Mauresmo, Henin-Hardenne, and Kim Clijsters; what kept her from passing them was her fitness. In 2006, her hard work earned her a little more speed and strength, and a lot more confidence. She’s not racing around the court like Steffi Graf, and she won’t do that next year either. But she doesn’t need to. A better comparison is Lindsay Davenport: Both women are 6 foot 2, but Sharapova moves a lot better than Davenport ever did and seems capable of more.

She should continue to improve her tennis, too. Her service return is already tops on the tour, and her serve is probably the best as well. Her forehand and backhand have never been a problem, though she could still learn to ease up on a few of the more difficult ones. (Perhaps she’ll even learn to knock off an easy volley before she retires.)

As Sharapova continues to progress, her rivals have reached their peaks and have nowhere to go but down. Consider the top three:

Mauresmo: She has been the best story of 2006. The 27-year-old Frenchwoman, known for her collapses under pressure, won two Grand Slam titles this year — both over Henin-Hardenne. At Wimbledon, she delivered a gutsy come-from-behind victory. Yet one does not get the sense that Mauresmo’s game is on the rise. Her forehand, which she hits with an extreme grip and lots of spin, allows bigger hitters like Sharapova to push her around and neutralize her athletic gifts. If Sharapova’s U.S. Open semifinal victory was any indication (two love sets), Mauresmo won’t be beating her too often in years to come. She’s also unlikely to defend her tour championships’ title this week after missing the last 10 days with an injured shoulder.

Henin-Hardenne: Mauresmo had a stellar season, but she wasn’t the best player this year. That honor goes to Henin-Hardenne, who reached the final of all four Grand Slams, defended her French Open title, compiled the best winning percentage on the tour, and helped Belgium reach the Federation Cup final. Sure, she retired in two of those matches (the Australian Open and the deciding Federation Cup doubles) but reaching all of them was an astonishing feat, especially for an undersized player who has spent many weeks on the sidelines in the last few years. Henin-Hardenne played the most matches against the other women in this week’s championships, and she had the best record: 15–5. That said, Henin-Hardenne, 24, had an uncommonly healthy year, and that’s unlikely to continue. The Belgian is small and injury prone, and any time off she needs to recover — or prevent her body’s further deterioration — will hurt her ranking. Unless she steadies her serve, she’ll have increasing trouble with Sharapova even when healthy, as she did in Flushing. Clijsters: Henin-Hardenne’s Belgian rival, Clijsters, 23, says she will retire at the end of next year. She won a tournament in Belgium yesterday after missing 10 weeks with an injury.

The rest of the contenders, including the other four who qualified for the tour championships and a handful of other youngsters, do not, as of yet, have what it takes to become dominant players. Perhaps the best prospect is Nicole Vaidisova, but she’s faded a bit since her fine French Open and is much like a young Sharapova when it comes to footwork and speed (her strokes are erratic, too). Jelena Jankovic and Ana Ivanovic, who had solid results in 2006, have too many flaws (and too little confidence) to play for the no. 1 ranking, at least at this point.

Whatever criticisms one has of Sharapova — one-dimensional, unsporting, too darn loud — one cannot knock her commitment to training and to success. She is the favorite this week, and a win would give her the no. 1 ranking unless Henin-Hardenne has an exceptional tournament (Sharapova is grouped with Clijsters, Svetlana Kuznetsova, and Elena Dementieva; Henin-Hardenne’s group includes Mauresmo, Nadia Petrova, and Martina Hingis). Otherwise, she’ll become no. 1 next year, and once she does, she likely won’t give it up for a long while, perhaps four or five years if she remains healthy. She clearly wants to be at the top, and she’s in the best position to get there and stay put.

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James Blake has qualified for his first Masters Cup, though he needed a lot of help to do it. Blake lost in round of 16 at the Paris Masters this week, but the man who beat him, Tommy Haas, retired with an injury in the semifinals, knocking him out of contention. Two other contenders for the final spot, Fernando Gonzalez and Mario Ancic, lost in the second round and quarterfinals.

One final note on the WTA Championships: This is the first year since the inaugural championships in 1972 in which no American woman qualified for the final eight. This year’s tournament has moved from ESPN to Versus.

tperrotta@nysun.com