TOKYO - Japan's Naomi Osaka is relishing her time at the Tokyo Games while other medal contenders have fallen away in the early rounds of the Olympic tournament.

The world number two, back on the court after pulling out of the French Open on mental health grounds and also missing Wimbledon, has been barely troubled in her first two matches at the event.

She brushed aside her opponents in straight sets and has been handling the outsized attention she is receiving on home soil with aplomb.

"I'm here for a good time," Osaka, who lit the Olympic flame at Friday's opening ceremony, tweeted on Monday after beating Swiss Viktorija Golubic 6-3 6-2 at Ariake Tennis Park.

The same could not be said of her closest rivals, with world number three Aryna Sabalenka of Belarus crashing out of the tournament on Monday after a tough, three-set encounter against an inspired Donna Vekic of Croatia.

Sabalenka's loss came a day after Australian number one Ash Barty was dumped out of the tournament in a stunning upset by Spain's Sara Sorribes Tormo. 

Two-time Wimbledon champion Petra Kvitova was also beaten on Monday, going out 5-7 6-3 6-0 to Belgian Alison van Uytvanck, while last year's French Open champion Iga Swiatek of Poland fell 6-3 7-6(4) to Spaniard Paula Badosa.

(Reporting by Rozanna Latiff; editing by Clare Fallon) ((rozanna.latiff@thomsonreuters.com; +61 3 9492 9423 ; Reuters Messaging: @rozlatiff on Twitter))