Naomi Osaka will return to the top of the women's tennis world rankings after Karolina Pliskova lost in the quarter-finals of the Rogers Cup in Toronto.

Pliskova, number one for eight weeks in 2017, needed to win the tournament to regain top spot but lost 6-0 2-6 6-4 to Canadian teenager Bianca Andreescu.

Ashleigh Barty replaced Osaka at the top in June, but the Australian's run ended with her loss in round two.

Osaka plays 23-time Grand Slam singles champion Serena Williams on Saturday.

Their quarter-final will be their first meeting since last year's US Open final when Williams argued with the umpire late in the match and Osaka was awarded a game as a penalty on her way to winning a first Grand Slam title.

Andreescu, 19, is currently 22nd in the rankings and will play Sofia Kenin in the semi-finals after the American defeated Ukrainian sixth seed Elina Svitolina 7-6 (7-2) 6-4.