Ashleigh Barty will get one last chance to secure the US Open top seeding after being usurped as world No.1 on Thursday.
Reigning Australian and US Open champion Naomi Osaka moved into poll position to regain top spot after breezing into the third round of the Canadian Open.
Osaka won the first set 6-2 against Tatjana Maria before the German retired injured, gifting the Japanese superstar a passage through to the last 16, where she will face Polish qualifier Iga Swiatek.
Barty’s 6-7 (7-5) 6-3 6-4 second-round loss to American Sofia Kenin on Wednesday had left the door open for either Osaka or Czech Karolina Pliskova to claim the No.1 ranking next week.
Pliskova also remains in the hunt after beating Alison Riske – the American who snapped Barty’s 15-match winning streak in the Wimbledon fourth round last month – in her opener.
Pliskova defeated Riske 6-4 6-7 (4-7) 6-2 and will face Anett Kontaveit, who advanced when Carla Suarez Navarro retired while trailing 7-5 3-1.
Either way, Barty’s eight-week stint as Australia’s first women’s world No.1 since Evonne Goolagong Cawley in 1976 will end on Monday.
If Osaka reaches the quarter-finals or semis, Pliskova will need to make the final, or otherwise defeat Osaka in the title decider to return to No.1 for the first time since 2017.
Barty, though, could regain top spot with a strong run next week in Cincinatti, after which the seedings for the season’s final grand slam in New York will be determined.
Meanwhile, three-time Toronto champion Serena Williams, seeking more matches before chasing a record-equalling 24th career grand slam title at Flushing Meadows from August 26, won her first outing since losing the Wimbledon final to Simona Halep.
The 37-year-old beat Belgian Elise Mertens 6-3 6-3 to reach the third round where she’ll face Russia’s Ekaterina Alexandrova, a 6-4 6-3 winner over Zhang Shuai.
Halep survived a stern test from American qualifier Jennifer Brady with a 4-6 7-5 7-6 (7-5) victory to reach the last 16 and keep alive her hopes of a second consecutive title in Toronto.
Next up for Halep, who won the event last year in Montreal, will be Russian wildcard Svetlana Kuznetsova, who beat Donna Vekic 7-6 (7-4) 6-3.
Sixth seed Elina Svitolina, who won in Toronto two years ago, beat Czech Katerina Siniakova 6-3 3-6 6-3, while fellow Ukraine Dayana Yastremska ousted former world No.1 Victoria Azarenka 7-5 7-5.