1st WTA title vaults Canada's Bianca Andreescu to No. 68

Australian Open champion Naomi Osaka is the first player from Asia to top the men's or women's tennis rankings while Canada's Bianca Andreescu jumped 38 positions to a career-high No. 68.

Osaka is the youngest woman to make her debut at No. 1 in nine years.

"I feel like I'm literally just still learning," the 21-year-old Osaka said. "Everyone kind of adjusts to being No. 1 in a different way."

Simona Halep's 48-week stay atop the WTA rankings ended Monday as she slid to No. 3 after a fourth-round loss to Serena Williams, one year after getting to the final at Melbourne Park.

"The main goal is just to play as good as I can every match, to win every match I play, so the ranking doesn't really matter," Halep said.

Andreescu, from Mississauga, Ont., defeated American Jessica Pegula in the final of the 125K Series Oracle Challenger at Newport Beach, Calif., on Sunday. It was her first career WTA Tour title.

Andreescu also became the top Canadian on the rankings list, moving ahead of Eugenie Bouchard of Westmount, Que. Bouchard rose three spots to No. 76.

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After struggling through a first set that lasted just 27 minutes, Andreescu broke Pegula for the first time to go up 3-2 in the second. The American replied with a break of her own to tie it at 4-all but Andreescu bounced right back with another break and held serve to set up the third and deciding set.

Halep said the year-end ranking is what is "more important" than where things stand now, "so I will not stress myself about this."

Osaka's second consecutive major title, following her success at the U.S. Open last year, helped her rise three spots.

She was born in Japan — her mother is Japanese, her father is Haitian — and moved to the United States when she was 3. She has dual citizenship and now is based in Florida.

Osaka is the youngest woman to reach the top since 2010, when Caroline Wozniacki did it at 20.

"People were talking about [me] being No. 1 if I win this tournament. I was able to accomplish that," Osaka said. "But the ranking was never my real goal. It was just to win this tournament."

The runner-up at Melbourne Park, Petra Kvitova, jumped from No. 6 to No. 2.

Sloane Stephens is No. 4, and Karolina Pliskova went from No. 8 to No. 5.

Williams missed the 2018 tournament after having a baby; her quarterfinal run this time pushed her up five places to No. 11.

Surprise semifinalist Danielle Collins, a 25-year-old from Florida, climbed from No. 35 to No. 23. The woman she upset in the fourth round, three-time major champion Angelique Kerber, dropped from No. 2 to No. 6.

Dominant Djokovic remains No. 1

Novak Djokovic's record seventh Australian Open title allowed him to stay at No. 1 in the ATP rankings, and Rafael Nadal's runner-up showing kept him at No. 2.

But 2017-18 champion Roger Federer's fourth-round exit took him from No. 3 down to No. 6.

The player who beat Federer, 20-year-old Stefanos Tsitsipas of Greece, turned his first run to a Grand Slam semifinal into a career-best ranking of No. 12.