News of the pending retirement of Serena Williams overshadowed proceedings at the tune-up for the year's final Grand Slam but there were no shortage of first-round upsets for fans to enjoy, including one by local Bianca Andreescu.
Twice U.S. Open champion Osaka, in only her second tournament back from an Achilles injury, battled on gamely before retiring while trailing Kaia Kanepi 7-6(4), 3-0. "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.
Toronto-born Raducanu conceded a tight first set to Camila Giorgi but looked on course to level up the contest when she took a 2-0 lead in the second.
The Italian defending champion stormed back to rattle off the last six games with a mix of solid returns, net play and movement, however, easing into the second round 7-6(0), 6-2. "I think it was a really good match, to be honest," said ninth seed Raducanu. "I just need to get better at dealing with players who play as quick as she does." Andreescu later delighted a packed house with a 7-6, 6-4 victory over Daria Kasatkina in an evening match that left the Russian world number nine, fresh off a title win in San Jose, clearly disgruntled.