MELBOURNE, Australia (AP) - Australian Open champion Naomi Osaka is the youngest woman to make her debut at No. 1 in nine years and the first man or woman from Asia to lead the tennis rankings.

Simona Halep's 48-week stay atop the WTA ended Monday. She slid to No. 3 after a fourth-round loss to Serena Williams.

Williams missed the tournament last year after having a baby; her run to the quarterfinals this time pushed her up five places to No. 11.

The 21-year-old Osaka's second consecutive major title helped her rise three spots.

Runner-up Petra Kvitova went from No. 6 to No. 2.

Men's champion Novak Djokovic remained No. 1 in the ATP rankings. Runner-up Rafael Nadal stayed at No. 2, but Roger Federer's fourth-round exit dropped him from No. 3 to No. 6.

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