"I have much better judgement than Clinton. I also have a much better temperament. I think my strongest asset by far is my temperament. I have a winning temperament."

Voters were looking to asses the "Presidential qualities" of both Donald Trump and Hillary Clinton last night, and while Donald Trump’s strongest asset my be his temperament, he was not the winner, writes RTÉ Washington Correspondent Caitríona Perry.

This debate saw classic Clinton and classic Trump. And it was a brawl.

Voters will have learned nothing new about either candidate, and also gleaned very little about the substance of their policies. But it was great television.

Audience figures still remain to be confirmed, but it is likely to beat the previous record held by the Reagan-Carter debate of 81 million in 1980.

Hillary Clinton was the clear winner, but expectations were so low in advance for Donald Trump that his performance could not really be considered "bad".

He had boasted about doing little preparation in advance for the debate and that showed in how he managed to tie himself in knots answering questions that he should have predicted - especially on his tax returns.

Proceedings began calm and controlled with both candidates appearing to be set for a policy debate but it quickly descended into mutual attacks and insults.

Mr Trump had the strongest start and landed early jabs on his opponent.

The first clash coming on the issue of trade and jobs with Mr Trump challenging Mrs Clinton on her flip-flopping policies over the Trans-Pacific Partnership and the North Atlantic Free Trade Agreement, which her husband signed into law when he was in office.

Mrs Clinton responded with a remark about how Mr Trump’s fortune was based on money he inherited from his father - he dropped his cool to remark that it was only a small loan.

The biggest clashes of the night though came from questions relating to Donald Trump's tax returns, his "birther" movement questioning the birthplace of Barack Obama, and whether he had initially supported the Iraq War.

These were all predictable questions, yet he did not have polished answers ready for any.

In a departure from the usual role of US debate moderators, NBC’s Lester Holt repeatedly pressed Mr Trump on some of these issues, for example debunking his statement that he could not release his tax returns until an audit was completed.

There was no such restriction, said Mr Holt. While Mrs Clinton speculated that it was because he was not as rich as he claimed, had not been as charitable as he should have been and owed Wall Street banks millions of dollars.

His response to this was to talk about how much his buildings were worth and how "underleveraged" he was.

When Mrs Clinton pressed Mr Trump suggesting he probably had not paid any federal income tax, he did not dispute that, and on another occasion said he was "smart" for not having federal income tax at another point in his career.

Both candidates are polling so closely and have such high unfavourability ratings that last night's performance is unlikely to have them many new voters, nor cost them many either.

They both held true to their respective public images.

The original bombastic Mr Trump returned, frequently interrupting Mrs Clinton and talking over her.

The former Secretary of State played her scripted part, polished and in control, but engaging in more defensive debating that she would have planned to.

She admitted she had made a mistake in having a private email server, and said she would not have made that choice if she had the time over.

She scored points from him by listing all the insulting terms he has used against women in the past, and he retorted that most of those had been aimed at Rosie O'Donnell, adding bizarrely that most people would agree she deserved it.

He also cryptically said at one point that he had "something extremely rough" to say about "Hillary and her family" before adding, "I can't do it, I can't do it".

He is not doing well with women voters, and those comments will not have helped, he is also doing badly with non-White voters, and that won’t have been changed with him stating that in US inner cities "African Americans and Hispanics are living in hell. It's so dangerous", and suggesting bringing back "stop and frisk" policies which have already been ruled as unconstitutional because of how it involves racial profiling, targeting minority communities.

For Mrs Clinton's part, voters will not have seen anything new, and her campaign team said they had prepared for a different debate where she could have laid out some policy issues, which she did not have the opportunity to do last night.

But this is only round one of three. Candidates are straight back on the campaign trail later this morning, before they go head to head again early next month.