Serena Williams, the 13-time grand slam winner, has plummeted to 175th on the WTA list, her lowest spot since 1997.
The former No 1 was ranked 25th entering Wimbledon after missing nearly a full year because of a series of health scares and her failure to defend her title at the All England Club meant she lost significant rankings points.
Her lost to Marion Bartoli in the fourth round effectively led to the 150-place slide yesterday.
Her older sister, Venus, who also lost in the fourth round last week, went from 30th to 34th, meaning that Bethanie Mattek-Sands, who stayed at 31st after a first-round Wimbledon exit, is the highest ranked US woman.
The last time someone other than one of the Williams sisters was the top American in the WTA rankings was January 2007, when Lindsay Davenport was ahead of them.
Caroline Wozniacki stayed at No 1 despite losing in the fourth round last week.
Petra Kvitova, the Wimbledon champion, rose one spot to No 7, while Maria Sharapova, the runner-up, also moved up one place, to No 5.
"Times are changing," Djokovic said yesterday. "It's good for the sport, I think, to have some new faces."
Federer first took the top place in 2004, and he or Nadal had been No 1 every week since.
"They have made me improve," Djokovic said. "They have made me a better player. Any athlete in the world dreams of being No 1 of the world. This is something that gives us a lot of motivation. So finally, when you really do it, and when you know that you're the best, it's just an amazing achievement."
Bernard Tomic, the Australian who became the youngest man to reach the quarter-finals at the grass court event since Boris Becker won a second consecutive Wimbledon title in 1986, leapt from 158th to a career-high 71st.
* Associated Press
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