Former world number one Naomi Osaka retired from her opening match at the Canadian Open in Toronto on Tuesday due to injury, sending veteran Kaia Kanepi through to the second round. Osaka pulled out of the match trailing 7-6 (7-4), 3-0 due to a back injury. “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,” Osaka said afterwards. “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.” Estonian Kanepi, who continued a good run after reaching the final of the Citi Ope…