Donald Trump has criticised the moderator in the first US presidential debate, Lester Holt, for being tougher on him than on Hillary Clinton.
The two candidates clashed over jobs, temperament and tax in a debate watched by tens of millions of viewers.
He also complained about his microphone crackling and being at a lower level than Mrs Clinton's.
Opinion polls give Mrs Clinton a slight edge, with a majority of voters declaring her the winner of the debate.
Although Mr Trump told reporters immediately after the debate that Lester Holt had done a good job, he later accused him of a left-leaning performance.
"He didn't ask her about the emails, he didn't ask her about the scandals, he didn't ask her about the Benghazi deal. He didn't ask her about a lot of things he should have asked her about. Why? I don't know," he said, speaking to the US news programme Fox & Friends the morning after the debate.
He said Mr Holt had been much tougher on him: "You look at it, you watch the last four questions, he hit me on birther [Mr Trump's past allegation that President Obama was not born in the US], he hit me on a housing deal from many years ago, that I settled on with no recourse and no guilt... that's a beauty to be asked, a 40-year-old lawsuit."
He also said his microphone was "terrible" and crackled, and that his volume was lower than Hillary Clinton's microphone. He blamed it for what some listeners thought were sniffles by Mr Trump during the debate.
Asked to rate Hillary Clinton's performance, he said he would give her a C plus but declined to grade himself. "I think I really did well when they asked normal questions," he said, but added he naturally struggled when asked "unanswerable" ones.
On what he might do differently: "I may hit her harder in certain ways. You know, I really eased up because I didn't want to hurt anybody's feelings. So I may hit her harder in certain ways."
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Hours before the programme, polls suggested the candidates were locked in a dead heat, adding to the tension between the rivals on stage throughout the debate.
"I have a feeling that by the end of this evening, I'm going to be blamed for everything that's ever happened," Mrs Clinton quipped when prompted to respond to one of Mr Trump's attacks.
"Why not?" Mr Trump interrupted.
"Yeah, why not," she answered. "You know, just join the debate by saying more crazy things."
Mr Trump was later thrown on the defensive by Mr Holt for not disclosing his tax returns.
He claimed he was under a "routine audit".
But the hotel developer promised he would release them if his opponent released 33,000 emails that were deleted during an investigation into her private email set-up while secretary of state.
Mrs Clinton made a brief response to Mr Trump's attacks about her use of a private email server - which has haunted her on the campaign trail. She said there were no excuses for the "mistake" and that she takes responsibility for it.
Mr Trump said his rival did not have the stamina to be president, to which Mrs Clinton replied that she visited 112 countries and endured an 11-hour congressional hearing as secretary of state.
In other debate highlights:
* Mr Trump said African-Americans are living "in hell" in the US due to gun violence.
* Mrs Clinton criticised him for saying climate change was a Chinese hoax
* She was attacked by him for being weak on Islamic State militants and soft on Iran
* "You've been fighting ISIS your entire adult life,'' Mr Trump mocked
* In a wider assault on his treatment of women, she said he had called women "pigs, slobs and dogs"