Number three seed Alexander Zverev said he "played horrible" after crashing out in the first round of the Japan Open on Monday, losing to world number 60 Jordan Thompson.
Germany's Zverev, ranked ninth in the world, lost 6-3, 6-4 in Tokyo, one week after falling at the first hurdle at the Shanghai Masters.
Zverev, who won the Chengdu Open in China last month, said there was "nothing that I did well" after having his serve broken three times by Thompson.
"Today, I played horrible," said Zverev.
"He played quite good, he served quite good but it's just a very, very bad match for me. I don't know what to say."
Zverev had said that illness contributed to his loss to Roman Safiullin in Shanghai, but Thompson had "made it tricky" for him.
The Australian lost in straight sets to Novak Djokovic at this year's Wimbledon but did not back down against Zverev.
"I haven't done anywhere near as much as he has but when I get on the court with these guys, I've got to believe that I can beat them," said the 29-year-old.
"If you don't believe it, you may as well not be out here, so I'm just really enjoying the challenge."
Zverev was returning to Japan for the first time since winning Olympic gold two years ago at the Tokyo Games, which were held behind closed doors because of the coronavirus pandemic.
He said it was "nice to play in front of spectators but I only played one match".
"I lost today so the feeling generally is not very great right now," he said.
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