Wimbledon champion Serena Williams officially moved up to No. 1 in the WTA Tour rankings Monday, the first time she's been ahead of older sister Venus.

Serena, 20, is the 11th woman to lead the computer standings since they started in 1975. She replaces Venus, who's had three stints at No. 1 for a total of 11 weeks since February.

It's the eighth change at the top this year.

Serena has won the last two Grand Slam tournaments, beating her sister in the finals of Wimbledon on Saturday and the French Open last month. She's 36-3 with a tour-leading five titles in 2002, and is currently on a season-high 19-match winning streak.

In the men's rankings, Wimbledon winner Lleyton Hewitt strengthened his hold on No. 1, while Pete Sampras -- who lost in the second round at the All England Club -- dropped three spots to 16th. A six-time year-end No. 1, Sampras hasn't finished a season out of the top 10 since 1989, his second as a pro.

The Williams sisters became the first siblings at 1-2 in the rankings after the French Open, where Serena reached a then-best of No. 2 and said: "She's No. 1 on paper. Hopefully, I can get there soon."

As long as they stay 1-2, regardless of the order, they will continue to be placed on opposite sides of tournament draws, meaning they could only face off in finals. The sisters have played for the title at three of the last four Grand Slam tournaments, and a Williams has won seven of the past 12 majors.

Three-time major champion Jennifer Capriati, who lost the No. 1 ranking after Roland Garros, stays at No. 3 this week, followed by Monica Seles, Kim Clijsters, Jelena Dokic, and Wimbledon semifinalist Justine Henin.

Martina Hingis slid to eighth, with Lindsay Davenport ninth and Wimbledon semifinalist Amelie Mauresmo 10th. Hingis and Davenport have been out with injuries.

Hewitt is followed by Marat Safin, Tommy Haas, Wimbledon semifinalist Tim Henman and Yevgeny Kafelnikov. Andre Agassi is the top U.S. player at No. 6, with French Open champion Alberto Costa seventh.

French Open runner-up Juan Carlos Ferrero, Australian Open champ Thomas Johansson, and Sebastien Grosjean complete the top 10.

Hewitt also leads the ATP Champions Race, a measure of a player's success from January to December. Safin is No. 2, followed by Henman, Costa and Agassi.