BRISBANE, Australia -- Naomi Osaka got an extended workout in her opening match at the Brisbane International just two weeks before the defense of her Australian Open title.
Osaka defeated Greece's Maria Sakkari 6-2, 6-7 (4), 6-3 on Tuesday to set up a second-round match with American Sofia Kenin.
The two-time Grand Slam champion and former world No. 1 took more than two hours and had 16 aces to beat Sakkari.
Elsewhere Tuesday, eighth-seeded Madison Keys beat Czech qualifier Marie Bouzkova 6-3, 6-2, and will face Sam Stosur in the second round.
"Sam's always tough," Keys said. "I think she's beaten me every time we have played. It's also hard to play someone who is going to be playing at home and have the crowd and all that."
Russian qualifier Liudmila Samsonova recorded the upset of the tournament so far by defeating American Sloane Stephens, the 2017 U.S. Open champion, 6-4, 2-6, 6-3.
Samsonova will next face two-time Wimbledon champion Petra Kvitova, who saw off Russia's Anastasia Pavlyuchenkova 2-6, 6-1, 6-0.
Anett Kontaveit breezed past Su-Wei Hsieh 6-4, 6-1 in just over an hour, and wild card Maria Sharapova came up short against American qualifier Jennifer Brady 3-6, 6-1, 7-6 (3) after over two hours on court.
Qualifier Yulia Putintseva defeated Donna Vekic 6-3, 3-6, 7-5 in two and a half hours, while No. 6 seed Kiki Bertens came from behind to beat Dayana Yastremska 4-6, 6-1, 6-3.