Tennis superstar Naomi Osaka returns to court with 1st-round win at Olympics

Naomi Osaka is back and still winning.

The Japanese superstar, who lit the Olympic cauldron, defeated 52nd-ranked Zheng Saisai of China 6-1, 6-4 on Sunday in her first match in nearly two months.

Osaka hadn't played since she withdrew from the French Open in May to take a mental health break, revealing that she had dealt with depression. She then sat out Wimbledon.

Osaka stopped to talk with reporters afterward, having said in Paris that she experiences "huge waves of anxiety" before meeting with the media and that she would be skipping news conferences.

"More than anything else I'm just focused on playing tennis," Osaka said. "The Olympics has been a dream of mine since I was a kid so I feel like the break that I took was very needed.

"I feel definitely a little bit refreshed and I'm happy again."

Osaka added that she was "happy" that reporters were asking her questions, then added: "I feel a little bit out of my body right now."

"There's nothing wrong with my body, I just felt really nervous," Osaka said. "I haven't played since France so there were definitely some things that I did a bit wrong but I think I can improve in the matches that I continue playing."

The second-ranked Osaka was sharp from the start, serving an ace down the T on the opening point of the match and and racing out to a 5-0 lead.

Wearing a bright red dress and a red visor and with her hair styled in red-and-white braids to match the colours of the Japanese flag stitched onto the left side of her chest, Osaka served six aces in all and produced 25 winners to Zheng's 10.

'Honoured' to light cauldron

Osaka's match was originally scheduled to open the tournament on Saturday but then was pushed back a day before her starring role in Friday's opening ceremony.

"I feel very very proud," Osaka said, revealing that Olympic organizers asked her to handle the cauldron honours back in March.

"When I lit the flame I was super honoured," she added. "I think that's a position that you dream about and not anyone can do it so for me when they asked me if I wanted to I was very surprised but very honoured and I'm just very happy to be here and very happy to play — especially in Tokyo.

Osaka will next face 50th-ranked Viktorija Golubic of Switzerland.

For other top players in the tennis tournament at the Tokyo Games, it wasn't so straightforward.

Top-ranked Australian Ash Barty was upset by 48th-ranked Sara Sorribes Tormo of Spain 6-4, 6-3. Barty remains in the doubles competition, having won with Australian partner Storm Sanders on Saturday.

Barty's singles defeat came 15 days after she won Wimbledon for her second Grand Slam title.

She struggled with a whopping 55 unforced errors to Sorribes Tormo's 13 and got in only 54 per cent of her first serves compared to her opponent's 83 per cent.

WATCH | Barty stunned by Sorribes Tormo:

Heat and humidity were issues again with the temperature rising to 33 C and the sun baking the hard courts at Ariake Tennis Park.

Also advancing was Wimbledon finalist Karolina Pliskova of the Czech Republic, who beat Alize Cornet of France 6-1, 6-3. Third-seeded Aryna Sabalenka of Belarus eliminated Magda Linette of Poland 6-2, 6-1.

Carla Suarez Navarro, the Spaniard who plans to retire this year, beat Ons Jabeur of Tunisia 6-4, 6-1 for her first victory since recovering from Hodgkin's lymphoma.

Camila Giorgi of Italy eliminated Jennifer Brady, the American who was this year's Australian Open finalist, 6-3, 6-2.

Among the men advancing were fourth-seeded Alexander Zverev of Germany, seventh-seeded Hubert Hurkacz of Poland and 12th-seeded Karen Khachanov of the Russian Olympic Committee (ROC).