US Open: Defending champion Naomi Osaka loses cool, bundled out by Canadian teen Leylah Fernandez

Two-time champion Naomi Osaka has suffered a stunning defeat to Canadian Leylah Fernandez 5-7 7-6(2) 6-4 in the third round of the US Open, ending her title defence inside Arthur Ashe Stadium.

Playing her first Grand Slam since pulling out of the French Open earlier this year, Osaka's return to Flushing Meadows did not go to plan, wordlessly leaving the court after uncharacteristically losing her cool in the second-set tiebreak.

The third seed whacked her racquet and then flung it onto the court twice in frustration, as Fernandez scored five straight points in the tiebreak.

Osaka did not receive a warning or a code violation, and left the court in between sets to regroup.

But her troubles continued, as the 18-year-old Canadian broke her serve to kick off the third set and Osaka hit a ball into the stands in the second game, prompting a warning from the chair umpire.

In the ninth game, Osaka rushed through her serves, not even waiting for the crowd to settle, but she was unable to create a single breakpoint opportunity in the final set.

Fernandez, who fired off 28 winners across the three sets, says she worked at "just finding the solutions".

"She's a great server, she's been hitting aces left, right and centre," says Fernandez, three days shy of her 19th birthday. "As I was getting closer to the baseline, I was like 'Oh, this is where I should be'."

A fan favourite in virtually any tennis venue, Osaka has struggled with uneven play, since she withdrew from Roland Garros earlier this year, amid a public row with tournament officials over media obligations, which she said had a negative impact on her mental health.

Fernandez is teamed with Kiwi Erin Routliffe for doubles, where they will face Americans Ashlyn Krueger and Robin Montgomery in the second round.

Reuters