LAS VEGAS - While the two previous clashes between Republican Donald Trump and Democrat Hillary Clinton have been eventful, the final presidential debate produced by far the most jaw-dropping moment of what has already been an unprecedented campaign.
Roughly an hour into the 90-minute debate in Las Vegas, Nevada, moderator Chris Wallace asked the billionaire if he would commit to accepting the result of the election on Nov 8, even if it turns out to not be in his favour.
Mr Trump, who had in past week been telling supporters that the election is rigged against him, shocked with his answer.
"I will look at it at the time. I'm not looking at anything now. I'll look at it at the time," he said, to exclamations from some in the debate hall as well as gasps throughout the media centre.
Mr Wallace even had to repeat the question to make sure Mr Trump was indeed questioning the integrity of US democracy.
"Sir, there is a tradition in this country - in fact, one of the prides of this country - is the peaceful transition of power and that no matter how hard-fought a campaign is, that at the end of the campaign that the loser concedes to the winner... Are you saying you're not prepared now to commit to that principle?" he asked.
Mr Trump doubled down: "What I'm saying is that I will tell you at the time. I'll keep you in suspense. Okay?"
That single answer overshadowed what had been Mr Trump's best debate performance and one of the more substantial clashes between the two major party candidates.
And it also tipped the scales on the night in favour of Mrs Clinton. Though this was not as one-sided as the first debate that Mrs Clinton won, it also wasn't as close as the second debate that Mr Trump edged.
Mr Trump did land some attacks, but Mrs Clinton's preparation once again showed. That her closing statement to voters was a positive one while Mr Trump went on the attack also spoke to the momentum that the Democrat's campaign is currently enjoying.
A CNN/ORC instant poll found 52 per cent of debate watchers thought Mrs Clinton won, while 39 per cent gave the night to Mr Trump.
An indication of how the night went came minutes after the debate ended, as surrogates from both campaigns flooded into the "spin room" to give their takes to journalists.
While Mrs Clinton's supporters praised her for her calm performance, Mr Trump's supporters had to try to revise their candidate's comments on the rigged election.
Republican National Committee spokesman Sean Spicer, for instance, insisted that Mr Trump would, in fact, accept the eventual result - despite what was said on stage.
"He is going to win this election soundly and this won't be an issue," Mr Spicer said repeatedly as reporters pressed him on the issue.
Debate analysts also picked out the remarks on the election results as the standout moment of the night.
Associate Professor Michael Green of the University of Las Vegas described the comments as "dangerous" and said it would likely turn undecided voters against the candidate at a time when he is supposed to be expanding his base.
"I think it turns them against him. It certainly does not pick up people who were thinking of whether to vote for him. It may appeal more to a small part of his base, but even today there are reports that people aren't really heeding his call. So I don't think this is going over very well," he said.
Mr Trump had started with poise and restraint, and communicated his positions on abortion and gun rights well. Neither Mrs Clinton nor Mr Trump interrupted or spoke over each other for the first 20 minutes - raising hopes that the duel would not be as ill-tempered than their previous match-ups.
That all changed when talk turned to hacked e-mails from Mrs Clinton's campaign chairman that were published by WikiLeaks. She pivoted away from the e-mails - many of them with embarrassing details about how her campaign operates behind the scenes - to talk about the conclusion from intelligence agencies that Russia was likely to be behind the hacks.
Mrs Clinton then launched the first personal attack of the night, calling Mr Trump a "puppet" for Russian President Vladimir Putin. That appeared to anger Mr Trump, and from that moment on, the insults started flying.
Both candidates interrupted each other frequently and Mr Trump even started interrupting the moderator mid-question. He also resumed a tactic he had started in the first debate of saying "wrong" every time he disagreed with something Mrs Clinton said.
He also had some good moments, using his quick wit, especially when he called out Mrs Clinton for dodging a question on a leaked e-mail that said she wanted open borders.
"That was a great pivot off the fact that she wants open borders, okay? How did we get on to Putin?" he said to laughter from the crowd.
But Mrs Clinton had some strong moments as well, especially when she took him to task for his treatment of women.
"Donald thinks belittling women makes him bigger. He goes after their dignity, their self-worth, and I don't think there is a woman anywhere who doesn't know what that feels like. So we now know what Donald thinks and what he says and how he acts toward women. That's who Donald is," she said.
The debate had been billed as a do-or-die event for Mr Trump, the last chance for the candidate to make a big impact on a race with just three weeks to go.
The initial consensus from analysts, though, is that he did himself more harm than good.
Despite putting in an otherwise strong performance, Mr Trump's shocking response on the likelihood of a rigged election will mean he remains a long shot for the White House.