Kim Clijsters officially replaced Serena Williams at No. 1 Monday, becoming the first woman to lead the rankings without having won a Grand Slam tournament.

Clijsters is the 12th player atop the WTA Tour’s computer rankings since they began in 1975, and she’s the first Belgian.

“This is a very special day I’ll never forget. No matter what will happen the rest of my career, no one will ever take that away from me,” said Clijsters, whose first full year on tour was 1999. “It’s something that I will always have on my resume.”

She won her tour-leading sixth title of the season Sunday in Carson, Calif., beating former No. 1 Lindsay Davenport 6-1, 3-6, 6-1 in the final.

Clijsters has reached at least the semifinals of all 14 tournaments she’s entered this season, including at the Australian Open, French Open and Wimbledon. But she made just one final at those events, losing the championship match at Roland Garros in straight sets to countrywoman Justine Henin-Hardenne.

Williams, in contrast, won titles at the Australian Open and Wimbledon, giving her five of the past six majors.

But Williams hasn’t played since Wimbledon, and left knee surgery Aug. 1 is expected to keep her sidelined about two months, meaning she will not be able to defend her U.S. Open title. Her older sister Venus also has been out of action since Wimbledon, because of a stomach muscle injury. She is down to No. 5 in the rankings, her lowest position since July 2000. The computer rankings are based on a player’s best 17 tournaments over the preceding 52 weeks.

, and Clijsters is being rewarded for consistency and for playing week in, week out.

She plays far more often than either Williams. This year, for example, Serena has played in only seven events, Venus in six.

The 44-point gap at the top is one of the smallest in rankings history. Clijsters has 6,039 points, Serena 5,995.

The margin between Serena and No. 3 Henin-Hardenne is 988 points; between Henin-Hardenne and No. 4 Davenport it’s 1,425.

“Rankings have never been my priority. As a young player, the pressure comes more from people around you to be No. 1,” Clijsters said. “To be in this situation now is incredible.”

Amelie Mauresmo is No. 6, followed by Jennifer Capriati, Daniela Hantuchova, Chanda Rubin and Anastasia Myskina.

In the men’s rankings, Andy Roddick’s first career Tennis Masters Series title lifted him from No. 7 to No. 4, while Andre Agassi stayed at No. 1.

Roddick beat 2002 Wimbledon runner-up David Nalbandian in straight sets Sunday at Montreal for his fourth title of the year.

Reigning Wimbledon champion Roger Federer moved up one slot to No. 2, 120 points behind Agassi. The Swiss star could have passed Agassi but lost to Roddick in the Montreal semifinals.

French Open winner Juan Carlos Ferrero slid to No. 3, followed by Roddick, Guillermo Coria, former No. 1 Lleyton Hewitt, Carlos Moya, Rainer Schuettler, Sebastien Grosjean and Paradorn Srichaphan.

AP-ES-08-11-03 1440EDT