Maria Sharapova has replaced injured American Lindsay Davenport as world number one.
The 18-year-old, who has won three titles this year, is the first Russian woman to reach the top of the WTA rankings since their inception in 1975.
Sharapova would have toppled Davenport earlier this month but was forced to pull out of the JPMorgan Chase Open because of a chest injury.
"It's a dream come true to become number one in the world," she said.
"The computer doesn't lie," she said. "You have to achieve something to get there and it's been an amazing two years.
"It's been all about hard work and dedication and the achievement has been amazing."