Denmark's Caroline Wozniacki will replace Serena Williams as No. 1 when the new rankings are released on Monday.
Wozniacki, 20, will become the first Dane, male or female, to hold the top ranking after a 6-3, 6-2 win over Petra Kvitova at the China Open in Beijing today.
"This is a real big step for me. To be the world No. 1 has always been a dream for me," Wozniacki said in an on-court interview at the Beijing Tennis Center. "It doesn't feel like it's real."
Wozniacki is the 20th player to top the rankings since they began in 1975 and the third in the last two years to do so without having won a Grand Slam title, following Dinara Safina and Jelena Jankovic.
The Dane said capturing a major title was her next target.
"That would be like a dream come true," she said.
Wozniacki has won 11 career titles, five of them this year, and has lost once in her last 21 matches.
She reached the U.S. Open final last year, losing to Kim Clijsters. Her best Grand Slam result this season was also in New York, where she fell in the semifinals.
The head of women's tennis described Wozniacki as "an inspiring young woman."
"It's not surprising that Caroline's incredible athleticism, discipline, dedication to training, and razor sharp focus have gotten her to No.1," WTA chairman and CEO Stacey Allaster said. "With the No.1 ranking, Caroline has joined a group of extraordinary players that have climbed to the pinnacle of the sport."
Williams, the Wimbledon and Australian Open champion, has not played competitively since capturing her 13th Grand Slam title at the All England Club in July.
The American has been sidelined by a cut on her foot but could make her return in Linz, Austria next week.
Organizers said on the WTA event's website that Williams' flight is booked and she is due to arrive in Linz on Sunday, but the American has until 1400 GMT on Friday to confirm her entry.