By Nick Georgandis
Tennisnow.com

The WTA Championships kick off in Doha tomorrow amid another shake-up in the rankings.

  With Serena and Venus Williams both now retired for the rest of the 2010 season, the dominant American sisters each slipped another spot in the rankings this week.

  Serena fell to third after landing in second just two weeks ago, replaced at No. 2 by Vera Zvonareva, who has a new career high-water mark for the third time in a month.

  Serena's fall isn't over, new No. 4 Kim Clijsters has closed to within 60 points of the 18-time Grand Slam winner. Since Clijsters didn't play Doha last year, even a slightly-good performance this week will have her sitting third when the dust settles.

For Jelena Jankovic, the struggle has been more about her game and less about her health. She fell from seventh to eighth this week, replaced by Samantha Stosur. Since being upset by Zvonareva in the fourth round at Wimbledon, Jankovic has gone just 6-8, losing to three players outside the Top 100, including No. 268 Zarina Diyas last week in Moscow.

Kremlin Cup winner Victoria Azarenka tightened her grip on No. 10 with the points influx, while runner-up Maria Kirilenko surged into the Top 20, up five spots to No. 19, one spot below her career-best reached in July of 2008. It was Kirilenko's first final since Barcelona in April of 2009.

The other big move in the Top 50 came from Luxembourg champion Roberta Vinci. The 27-year-old Italian jumped from 45th to 38th with her surprising victory. It was her first title since Luxembourg in 2009.
At press time, the WTA had yet to reveal the two groups of play for the WTA Championships.

On the men's side of things, Roger Federer notched the crown at Stockholm while Victor Troicki earned his first pelt at the Kremlin Cup. Federer's triumph allowed him to maintain a 300-point lead on Novak Djokovic for No. 2 in the world.

There was only one move in the Top 10 -- Andy Roddick re-took ninth with Mikhail Youzhny falling to 10th. Youhzny did not play the Kremlin Cup because of a viral infection after winning it a year ago, losing 250 points in the process to the idle American.

Falling in the "this ranking system is really confusing" category, Marco Baghdatis fell a spot to 20th in this week's docket despite reaching the finals in Moscow. Nevertheless, he lost 100 points because a year ago he won the 250-point Stockholm event.

Benefitting from his fall was John Isner, who gained a spot to 19th. Kremlin winner Troicki vaulted 10 spots to 33rd, the biggest jump in the Top 50.

There are another 750 points up for grabs this week as the men compete in St. Petersburg, Vienna and Montpellier.