The big question going into the the first US presidential debate - a 90-minute encounter that had the power to decide the future of the world - was which Donald Trump would show up.

Would it be the subdued, disciplined candidate, seeking to prove his credentials for the highest office in the land, or would it be the street fighter who brawled and bullied his way to victory in the Republican primaries?

Within moments of the debate starting, it was clear it was the latter. But if the testy Republican candidate thought he was going to have things all his own way, he was wrong. Hillary Clinton, well prepared and on-message, threw as many punches as Mr Trump, dodged some of his swings, and landed some solid blows of her own. She may even have come out ahead, based on expectations going in.

By the end of the evening, the pair had probably each punched enough to please their own supporters. But it will be some days before the public learns if either of them won over any undecideds. It may be that this hugely-hyped television event - one that 100m people were expected to watch - changed very little in voters' minds. A CNN/ORC snap poll said 62 per cent of respondents felt Ms Clinton won, and 27 per cent believed Mr Trump was the winner.

“Donald, it’s good to be with you,” Ms Clinton said, as the pair shook hands as they arrived on the stage.

US election 2016: the race for the White House in pictures Show all 12 1 /12 US election 2016: the race for the White House in pictures US election 2016: the race for the White House in pictures Republican U.S. presidential nominee Donald Trump shakes hands with Democratic U.S. presidential nominee Hillary Clinton at the conclusion of their first presidential debate at Hofstra University in Hempstead, New York Reuters US election 2016: the race for the White House in pictures President Barack Obama embraces Democratic nominee Hillary Clinton on stage at the party's convention in Philadelphia US election 2016: the race for the White House in pictures Donald Trump's wife Melania delivered a speech at the GOP convention in Cleveland that was later found to have been cribbed in part from Michelle Obama's 2008 convention address AP US election 2016: the race for the White House in pictures Hillary Clinton talks to reporters aboard her new campaign plane on Labour Day, 5 September, her first 'press conference' since 2015 (Getty Images) US election 2016: the race for the White House in pictures Donald Trump held a joint press conference with Mexican leader Enrique Pena Nieto in Mexico City in August, hours before reiterating his harsh immigration plans at a campaign rally in Arizona Reuters US election 2016: the race for the White House in pictures Bernie Sanders officially endorsed Hillary Clinton, saying his progressive vision for ‘a transformed America’ would be ’best served by the defeat of Donald Trump’ Reuters US election 2016: the race for the White House in pictures Khizr and Gazala Khan appeared at the DNC to slam Trump for his stance on Muslim immigration, citing the case of their son Humayun Khan, who was killed in combat while serving as a Captain in the US Army in Iraq US election 2016: the race for the White House in pictures Libertarian candidate Gary Johnson is doing better in polls than any third party candidate since Ross Perot, 20 years ago Nicholas Kamm/AFP/Getty US election 2016: the race for the White House in pictures Green Party candidate Jill Stein (centre) marches with supporters in Colorado AP US election 2016: the race for the White House in pictures Hillary Clinton and Virginia Senator Tim Kaine at a rally in Kaine's home state in July, days before Ms Clinton tapped him to be her running mate Getty US election 2016: the race for the White House in pictures Trump on the campaign trail with his vice presidential pick, Indiana governor Mike Pence AP US election 2016: the race for the White House in pictures Former Ukip leader Nigel Farage appears at a Trump rally in Mississippi in August, where he told the crowd that he 'wouldn't vote for Hillary Clinton if you paid me'.

That brief moment was about the only polite interaction of Monday night. Over the next 90 minutes, he accused of her being an establishment politician who had achieved nothing during her lengthy career. He said contrary to what people may have learned in the mainstream media, he had “a better temperament” than his rival. “I have a winning temperament,” he said.

Republican U.S. presidential nominee Donald Trump speaks as Democratic U.S. presidential nominee Hillary Clinton listens during their first presidential debate at Hofstra University in Hempstead, New York, U.S., September 26, 2016 (Rick Wilking/Reuters)

She, in turn, sought to highlight him as a failed businessman who would do nothing to help America progress. He was not interested in science and ignored facts that did not suit his case. "Donald, I know you live in your own reality." she said.

Ms Clinton said that Mr Trump was a man with a “cavalier attitude” who could not be trusted to remain calm when dealing with difficult diplomatic situations.

“A man who can be provoked by a Tweet she not have his finger near the nuclear code,” she said.

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Ms Clinton demanded to know why Mr Trump would not release his tax returns, something every president has done in modern history. Mr Trump said he was unable to because he was being audited by the tax authorities.

“This is something the American people have a right to see. I don’t think he will because he he trying to hide something,” she said, in one of her clearly rehearsed lines that landed with a genuine zing.

“He is either not as rich as he says, he is not as charitable, he maybe doesn’t want the American people that he has paid nothing in federal income taxes.”

Mr Trump responded by saying: “[That] makes me smart.”

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The New York tycoon throw down his own gauntlet to Ms Clinton. “I will release my tax returns when she releases her 35,000 emails,” he said.

He said that Mr Trump did not believe Ms Clinton had “the stamina” required to be president. “I don’t think that Hillary has the stamina,” he said.

She responded: Well, when he travels to 108 countries and negotiates deals….he can talk to me about stamina.”

Mr Trump came back: “I admit she has experience, but it’s bad experience.”

Moderator Lester Holt asked Mr Trump about his long-standing campaign to try and prove that President Barack Obama was not born in the US. The president was born in Hawaii, but it was only this month that Mr Trump admitted this.

Mr Trump repeated his false accusation that Ms Clinton's failed 2008 presidential campaign against Mr Obama had initiated the so-called “birther” issue.

“Nobody was pressing it, nobody was caring much about it…I was the one that got him to produce the birth certificate and I think I did a good job,” he said.

Ms Clinton back: “He has really started his political activity based on this racist lie that our first black president was not an American citizen. There was absolutely no evidence for it. But he persisted. He persisted year after year."