The final US presidential debate began in unusually subdued fashion, but it didn't take long for normal service to resume.

Candidates Hillary Clinton and Donald Trump sparred on a number of topics and produced enough soundbites to keep all observers watching.

Here are the key moments from the debate.

1. Will Trump accept results?

Hours before the debate, Mr Trump's daughter Ivanka assured MSNBC that her father would accept the result of the election if he does not win.

During the debate, Mr Trump blasted those hopes aside. When the question was put to him directly by moderator Chris Wallace, Mr Trump refused to say that he would accept the result of the election.

"I will look at it at the time," he said. Pressed further, he went on: "I will tell you at the time. I'll keep you in suspense."

2. Everything is rigged

Responding directly to Mr Trump's comments about the election being rigged, Mrs Clinton came out swinging.

Calling what he said "horrifying", she accused her opponent of falling back on calling things rigged as soon as something doesn't go his way.

"Every time Donald thinks things are not going in his direction, he claims whatever it is is rigged against him," she said, citing the examples of him calling the Federal Bureau of Investigation into her e-mails and the Wisconsin Republican primary that he lost rigged.

Mrs Clinton ended with a tale from Mr Trump's former life as a reality TV personality. "There was even a time when he didn't get an Emmy for his TV programme three years in a row and he started tweeting that the Emmys were rigged against him."

Mr Trump couldn't resist interjecting: "Should have gotten it."

3. Who's the puppet?

Russia's role in influencing the US presidential election has come up from time to time, and it led to one of the most heated exchanges in Thursday's debate.

"(Russian President Vladimir) Putin, from everything I see, has no respect for this person," Mr Trump blasted, pointing at Mrs Clinton.

"That's because he'd rather have a puppet as president of the United States," she shot back.

Mr Trump jumped in with "no puppet, no puppet, you're the puppet, no you're the puppet" as Mrs Clinton continued about Mr Trump's links to Russia.

If you're counting, the "puppet" count is 4-1 to Mr Trump.

4. Donald and women

Mr Trump's attitude towards women has been one of the biggest issues of his campaign. At Thursday's debate, he claimed that the women accusing him of making unwanted sexual advances only wanted fame, and then blamed Mrs Clinton's campaign of orchestrating their efforts.

"I didn't even apologise to my wife because I didn't do anything," he added.

Mrs Clinton responded powerfully: "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."

Mr Trump then repeated something he's said before, to guffaws from the crowd: "Nobody has more respect for women than I do. Nobody."

Moderator Chris Wallace had to admonish the audience, "Please, everybody," he said.

5. Some bad hombres

There are some bad, bad drug lords in the United States, said Mr Trump, and he plans to kick them out of the country.

But it was his choice of words that left the Internet in a tizzy.

"We have some bad hombres here and we're gonna get them out," he said.

Cut the Internet - #BadHombres began trending on Twitter, with thousands joining the pile-in.

Some accused Mr Trump of being a, well, bad hombre himself.

6. Trump's crocodile tears

Calling the illegal dumping of aluminium and steel into the US by China one of the biggest problems, Mrs Clinton turned the heat on Mr Trump.

She said: "Donald has bought Chinese steel and aluminium. In fact, the Trump hotel right here in Las Vegas was made with Chinese steel.

"So he goes around with crocodile tears about how terrible it is, but he has given jobs to Chinese steel workers, not American steel workers."

7. A nasty woman

In one of the most blatant personal attacks of the debate, Mr Trump interrupted Mrs Clinton to say: "Such a nasty woman."

She had taken a jab against him for his alleged attempts to evade paying taxes in the midst of talking about her plan to raise taxes for the wealthy.

Reaction exploded online, with many saying they were proud to be nasty women, reclaiming the insult as a point of pride.

To her credit, Mrs Clinton appeared unfazed.

8. On abortion rights

Mr Trump said he would support seeing the 1973 landmark ruling that made abortion legal overturned. Choosing emotive language to describe his stance on the abortion issue, he said that Mrs Clinton's view would mean that "in the ninth month, you can take the baby and rip the baby out of the womb of the mother just prior to the birth of the baby".

He went on: "You can say that that's okay, and Hillary can say that that's okay, but that's not okay with me."

Mrs Clinton responded: "Using that kind of scare rhetoric is just terribly unfortunate."

And she stuck to her guns: "I will defend women's rights to make their own health care decisions. We have come too far to have that turned back now."