Ash Barty's shock loss sparks crazy scrap for World No.1 ranking

Ashleigh Barty's eight-week reign as the WTA's No.1 player in the world is officially over after Naomi Osaka breezed past her German opponent in the second round of the Canadian Open.

Barty left the No.1 ranking hanging by a thread after a shock first-up loss to Sofia Kenin on Tuesday, and Osaka has now swooped in.

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The Japanese star advanced after Tatjana Maria retired hurt after dropping the first set 6-2.

Barty's 6-7 (5-7) 6-3 6-4 loss to Kenin in her first match of the American hardcourt season left the door wide open for world No.2 Osaka to regain the top ranking.

The reigning US Open and Australian Open champion, Osaka will now almost certainly return to No.1 when the rankings are updated.

However former world No.1 Karolina Pliskova can also reclaim the top ranking this week for the first time in almost two years.

If Osaka reaches the quarter-final or semi-final in Toronto, Pliskova would need to reach the final, or otherwise defeat her in the final to be No.1.

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.

Pliskova, the first Czech ever to hold the top spot, opened her campaign in Toronto perfectly by beating Alison Riske, the American who snapped Barty's long winning streak in the Wimbledon fourth round last month.

The Czech defeated Riske 6-4 6-7 (4-7) 6-2 and will next face Anett Kontaveit, who's previous opponent Carla Suarez Navarro retired while trailing 7-5 3-1.

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.

Barty remains unfazed

Barty’s reign as World No.1 lasted just eight weeks, but she brushed off her shock loss as rust.

"I think it was a little rust but I think just in general it was just a bit loose," Barty said.

"At times I was missing by big margins, which is not something that I'm used to or comfortable with, but it's not panic stations.

"It's my first match on hardcourt in a long time."

Barty had beaten the 29th-ranked Kenin three times this year.

But the 20-year-old got the better of the Aussie on centre court at Aviva Centre to earn the fourth top-10 win of her career.

"It's very different conditions here and different coming from home, training in winter at the moment, where the ball is a little lower and here it's quite lively and quick off the racquet," Barty said.

"All in all, I didn't adjust well enough or quick enough to the conditions how I needed to."

with agencies