<div><span style="font-size: 1rem;">Four-time Grand Slam champion Naomi Osaka retired from her opening match on Tuesday at the WTA Toronto Masters with lower back pain, raising injury concerns with the US Open looming.</span><br></div><div><br></div><div>Estonia's Kaia Kanepi advanced when Osaka retired trailing 7-6 (7/4), 3-0. Kanepi, a runner-up last week in Washington, needed 71 minutes on court as she broke three times before the Japanese star called it quits.</div><div><br></div><div>Defeat drove the emotional Osaka to tears.</div><div><br></div><div>"I felt my back from the start of the match and despite trying to push through it, I just wasn't able to today," Osaka said.</div><div><br></div><div>"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."</div><div><br></div><div>Osaka has played only six matches with a 2-4 record since losing the Miami final in early April to world number one Iga Swiatek.</div><div><br></div><div>Kanepi, 37, won their only prior meeting five years ago in three sets at the US Open.</div><div><br></div><div>"I tried to play my game and stay aggressive. It was a very tight match," Kanepi said. "I felt I needed a little more time to get used to new things, but after that I felt comfortable."</div><div><br></div><div>Reigning US Open champion Emma Raducanu of Britain exited in the first round, losing 7-6 (7/0), 6-2 to Italy's Camila Giorgi.</div><div>Despite the setback in the city of her birth 19 years ago, Raducanu kept her spirits up as her US Open title defence draws nearer.</div><div><br></div><div>"It was a really good match, to be honest," Raducanu said. "The level was pretty high, especially in the first set.</div><div><br></div><div>"Camila's a great opponent. She won this tournament last year. I just need to get better at dealing with players who play probably as quick as she does "</div><div><br></div><div>Defending WTA Canadian champion Giorgi won a combative first set and ran away with the second against the 19-year-old Englishwoman, whose title defence in New York begins in less than three weeks.</div><div><br></div><div>The feisty Italian trailed by a break in both sets but showed her spirit by winning the last six games of the contest.</div><div><br></div><div>Giorgi needed just over an hour and three-quarters to advance to the second round over the ninth seed who broke into the ranking top 10 less than a month ago.</div><div><br></div><div>Raducanu had to hold on in a wild opening set, where serve was broken in six of the dozen games played.</div><div><br></div><div>The Briton saved a set point in the 12th game to bring on a tiebreaker, but collapsed to lose seven straight points as Giorgi took the set after 71 minutes.</div><div><br></div><div>Raducanu was broken three times in the second set as Giorgi finished off her victory.</div><div><br></div><div>bnbd24/fas</div>