Naomi Osaka retiredwith lower back pain from her opening match while defending champion Camila Giorgi beat Britain’s Emma Raducanu on Tuesday at the Toronto Open.

Osaka, in only her second tournament back from a left Achilles injury, retired while trailing Estonia’s Kaia Kanepi 7-6 (7-4), 3-0 in her first match of the US Open tune-up event.“I felt my back from the start of the match, and despite trying my best to push through it I just wasn’t able to today,” said Osaka.

“I’d like to pay credit to Kaia for playing well and want to wish her all the best for the rest of the tournament.”Osaka took a medical timeout in the first set and then spent more time working with the trainer during the changeover between sets. She fell behind in the second before deciding to end the match.“It’s very tough to see that she has to retire this way,” Kanepi, who will face Spanish eighth seed Garbine Muguruza in the second round, said during her on-court interview.US Open champion Raducanu went ahead 2-0 in the second set but Giorgi finished with a flourish.

“This is my game and so I should play like this always but sometimes it doesn’t work,” Giorgi said during her on-court interview.The two players exchanged six breaks of serve during the opening set before Giorgi flicked a switch and breezed through a tie-break that came to a quick end after a Raducanu double-fault.Up next for the 30-year-old Italian will be Belgian Elise Mertens, who was a 7-6 (7-2), 6-1 winner over Hungary’s Anna Bondar.Also reaching the second round was 10th seed Coco Gauff, China’s Zheng Qinwen,Belgian Elise Mertens and Spain’s Sara Sorribes Tormo and Australia’s Ajla Tomljanovic.