Australia's Ash Barty has reclaimed the number one spot in the WTA rankings less than a month after losing it while U.S. Open champion Bianca Andreescu moved up to a career-high fifth after her maiden Grand Slam win in New York.

Andreescu beat Serena Williams 6-3 7-5 in Saturday's final to maintain a 13-match unbeaten run, where she also won the Canadian Open, to break into the top 10 for the first time in her career.

"I don't want to take anything for granted. These are the moments you live for and I'm just beyond blessed," Andreescu, who moved up 10 places, told Reuters.

After taking the first set and leading 5-1 in the second, Andreescu was broken twice by 23-times Grand Slam winner Williams before eventually breaking back and winning the contest to become the first Canadian to win a major in the professional era.

"It definitely wasn't easy in the final against Serena Williams," the 19-year-old added. "I think I'm most proud of how I'm able to get into my zone and I was able to block out the crowd too because they were really, really loud.

"If I didn't do that, I'm sure Serena would have won that second set so I'm really glad with how I handled everything."

French Open champion Barty exited the tournament in the last 16 but regained the number one spot after last year's champion Naomi Osaka was also knocked out at the same stage.

The Japanese, who also beat Williams in last year's final, slipped to fourth in the rankings with Czech Republic's Karolina Pliskova and Ukraine's Elina Svitolina leapfrogging her to move up to second and third respectively.

Wimbledon champion Simona Halep fell two places down to sixth while Williams fell one spot to ninth despite her run to the final.

In the ATP rankings, there was no change in the top three with Novak Djokovic leading men's champion Rafa Nadal, who won his 19th Grand Slam on Sunday, and Roger Federer but this year's runner-up Daniil Medvedev moved up to a career-high fourth.

Medvedev has had a stellar record since a third-round exit at Wimbledon, reaching the finals of his last four tournaments, winning the Cincinnati Masters last month.