US and Australian Open champion Naomi Osaka returned to the world number one spot in the WTA rankings on Monday.

The 21-year-old lost to Serena Williams in the quarter-finals of last week's Rogers Cup but benefitted from the second-round defeat of former number one Ashleigh Barty and the failure of Karolina Pliskova to reach the semis in Toronto.

Osaka first hit top spot in January, after winning back-to-back majors in New York and Melbourne, making history as the first Japanese player to achieve it.

After seven weeks on top, Barty slips to second with Pliskova in third.

The only other movement in the top 10 sees Williams, a finalist in Toronto, climbing two places to eighth with Sloane Stephens going in the other direction.

Canadian Bianca Andreescu, who won the Rogers Cup following Williams' withdrawal with back spasms in the opening set of the final, climbs 13 places to 14.