Ash Barty has lamented a "loose and erratic" effort after she lost to Spain's Sara Soribes Tormo in the first round at the Tokyo Olympics.
The world number 48 dealt her biggest blow of the Games ever by defeating world number one and Wimbledon champion Barty 6-4, 6-3 as the Australian broke down in the scorching heat of Tokyo.
Barty made 55 unforced errors in the Spaniard's 13, completely ruled out 15 days after the Queenslander secured his second Grand Slam title.
"It was a tough day. A depressing day. I can't lie about it," she told Seven Network.
"I can't hide behind the fact that I wanted to do really well here. Today was not my day.
"Just loosen up. I knew I wanted to try to move the match [and] it would be a fine line of not pushing too hard and not getting into patterns I didn't want to get stuck in."
"(I was) very uncertain."
In scorching, humid conditions, men's No. 1 Novak Djokovic called for the match to start later in the day after his first-round win on Saturday.
Although the schedule remained the same on Sunday, a concession was granted with a longer break on the change of ends as part of the extreme weather policy.
"It's brutal, like an Australian summer (but) I enjoy the warmth and love of playing here in these conditions. It wasn't meant to be," Barty said.
That leaves Barty's medal hopes resting on doubles after a win on Saturday with Storm Sanders reaching the second round.
Naomi Osaka's exit opened the door for Naomi Osaka's gold medal after making quick work of her first match in nearly two months.
The Japanese superstar, who burned Olympic oysters, defeated China's Zheng Saisai 6-1, 6-4, ranked 52nd.
It was Osaka's first match since she withdrew from the French Open and sat out of Wimbledon to take a mental health break while she revealed she had dealt with depression.
Ajla Tomljanovic enjoyed victory on her Olympic debut, with the Australian leading 7-5 3-2 before Yaroslava Shvedova retired.
Max Purcell made the most of his incredible growth from the Tokyo audience to a last-minute call-up by defeating world number 15 Felix Auger-Aliassim 6-4 7-6 (7-2).
Purcell joined the team last week after Alex de Minaur tested positive for COVID-19, but was only due to play doubles before Andy Murray was injured hours before his match.
James Duckworth will join him and Aussie teammate John Millman in the second round of men's singles, world No. 77 as Slovakia's Lukas Klein with a 5-7 6-3 7-6 (7-4) win. Prosperous year continued. .
A late replacement in singles for the injured Marten Fuskovics, Australian Luke Saville was beaten 6–2 6–4 by Hubert Herkász.