NEW YORK - Garbine Muguruza made her debut at No. 1 on Monday, joining U.S. Open champion Rafael Nadal in making Spain the first country since the United States 14 years ago to top the WTA and ATP rankings.
Andre Agassi and Serena Williams were both No. 1 in 2003.
Muguruza, the Wimbledon champion in July, rose two spots Monday from No. 3 after getting to the fourth round at Flushing Meadows for the first time. She is the 24th woman to lead the WTA since it introduced computer rankings in 1975 - and the second Spaniard, after Arantxa Sanchez Vicario.
Muguruza takes over at No. 1 from Karolina Pliskova, who fell to No. 4 with a quarterfinal defeat in New York one year after finishing as the runner-up. Entering the U.S. Open, eight women had a chance to top the rankings by the end of the tournament.
The day she won Wimbledon for her second major championship, Muguruza was asked about what sort of priority she placed on getting to No. 1.
"My motivation is just to be able to be a good tennis player - a good tennis player, and to come to the Grand Slams and be a threat. The ranking is temporary," she said at the time.
"I don't know what it feels to be No. 1. Hopefully one day I can. And then I (will) compare," Muguruza said. "But for now, I'd rather be (No.) 10 and win Grand Slams, than be No. 1."
The woman who won the year's last Grand Slam tournament, Sloane Stephens, jumped to No. 17 from No. 83 by beating Madison Keys 6-3, 6-0 in the U.S. Open final Saturday, continuing her quick rise after having surgery on her left foot in January and going 11 months between tour appearances. Stephens was outside the top 900 at the start of August.
Simona Halep stayed at No. 2 on the WTA list, while Venus Williams' semifinal run in New York pushed her up four spots to No. 5, her first time in the top five since January 2011.