Ash Barty says she will keep fighting for an Olympic gold medal despite her shock opening-round defeat by Sara Sorribes Tormo in Tokyo.
The world number one fell at the first hurdle at Arianke Tennis Park, going down 6-4 6-3 against her Spanish opponent.
There were no such problems for Naomi Osaka; the home favourite overcame China's Zheng Saisai in straight sets.
BARTY TO KEEP FIGHTING FOR GOLD MEDAL
Crowned Wimbledon champion this month, Barty was unable to build on that momentum; amassing a whopping 55 errors.
World number 48 Sorribes Tormo took full advantage to set up a second-round showdown with France's Fiona Ferro.
Although frustrated by the manner of her defeat in the Japanese capital, the Australian's gold medal hopes are not over yet as she appears alongside good friend Storm Sanders in the doubles event on Monday.
"I'm disappointed I wasn't able to get through," she said. "I never really felt comfortable out there and wasn't able to play the match on my terms.
“The key to my game is serving well and I wasn't able to do that. I was a bit erratic and made too many errors.
"I'm excited to get back out there with Storm and to keep fighting for that gold medal."
OSAKA BEGINS WITH A WIN
Home favourite Osaka avoided joining Barty; the second seed seeing off Chinese opponent Zheng 6-1 6-4 in her first match since withdrawing from the French Open to book a date with Switzerland's Viktorija Golubic in round two.
Fifth and seventh seeds Karolina Pliskova and Garbine Muguruza also prevailed in straight sets against Alize Cornet and Veronika Kudermetova respectively, as did two-time Wimbledon champion Petra Kvitova against Jasmine Paolini.
Fourth seed Elina Svitolina was taken to a deciding set by Laura Siegemund, but held her nerve to prevail as a 6-3 5-7 6-4 winner.
SOLID SABALENKA SERVICE
Meanwhile, third seed Aryna Sabalenka eased to a 6-2 6-1 victory over Poland's Magda Linette.
The Belarusian, who reached the Wimbledon semi-finals, looked impressive as she won 25 of her 27 service points along the way.
But there was no joy for Ons Jabeur – who reached the last eight at SW19 – with the Tunisian losing in straight sets to Spain's Carla Suarez Navarro.
Also bowing out in the opening round were 11th and 12th seeds Jennifer Brady and Elise Mertens – beaten by Camila Giorgi and Ekaterina Aleksandrova respectively.