Here are five key highlights of the showdown:
Donald Trump went there, big league.
After holding his tongue in the first debate, Trump assailed Clinton's husband Bill, reminding television viewers about a string of accusations of sexual misconduct, including one of rape, leveled against the former president decades ago.
Fighting the backlash against his 2005 hot mic remarks in which he was caught saying he can grope women because those with celebrity status can "do anything," Trump's point was clear: a certain Clinton has done more than just talk.
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"Mine are words, his was action," he said, claiming that there has "never been anybody in the history of politics in this nation that's been so abusive to women."
In a pre-emptive strike before the debate, Trump met with three women who have accused Bill Clinton of unwanted sexual advances, including Juanita Broaddrick, who claims Clinton raped her in 1978.
Driving up the tension, the women were seated in the audience during the debate, as was Bill Clinton himself.
Trump entered the showdown at the nadir of his 16-month campaign, walloped by the release Friday of a leaked tape that captured him saying vile things about women.
In the debate's opening minutes he dismissed them as "just words" and "locker room talk." Clinton disagreed.
"He has said that the video doesn't represent who he is," Clinton, standing just a few feet from Trump, said calmly. "But I think it's clear to anyone who heard it that it represents exactly who he is, because we've seen this throughout the campaign."
Trump acknowledged he was "embarrassed" about his comments. "But I have tremendous respect for women."
Asked directly if he had done the things he mentioned in the video, Trump said: "No, I have not."
But Clinton once more questioned Trump's fitness for the Oval Office, saying it was not just the video that raises concerns about him.
"He has also targeted immigrants, African Americans, Latinos, people with disabilities, Muslims, and others."
Clinton's emails are not going away in 2016. Trump highlighted them in the debate, claiming that her use of a private server while she was secretary of state, and the sending of sensitive national security data, was grounds for imprisonment -- and that he would ensure she served time.
"If I win, I'm going to instruct the attorney general to get a special prosecutor to look into your situation, because there's never been so many lies," Trump fumed. "It's a disgrace."
Clinton responded by saying it was "awfully good" that someone with Trump's temperament was not running the country.
"Because you'd be in jail," Trump interrupted, in the most extraordinary outburst of the evening.
Back in July, Trump caused a firestorm when he invited Russia to unearth Clinton's missing emails from her time at the State Department. Then on Friday, the White House formally accused Russia's government of stealing and releasing emails from the Democratic National Committee.
Clinton seized on the controversy. "We have never in the history of our country been in a situation where an adversary, a foreign power, is working so hard to influence the outcome of the election."
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Noting her rival's praise of Russian President Vladimir Putin, Clinton suggested that Moscow was seeking to "influence the election for Donald Trump."
"Maybe because he says he agrees with a lot of what Putin wants to do, maybe because he wants to do business in Moscow," she added.
Trump batted away the accusations, saying Democrats "always blame Russia" and were trying to "tarnish" him through association with the country.
The night's final question -- for the candidates to each name something positive about the other -- took some sting out of the battering-ram nature of the race.
"I respect his children," a smiling Clinton stated, looking at Ivanka, Eric and Donald Trump, Jr and describing them as "incredibly able" and devoted. "I don't agree with nearly anything else he says or does, but I do respect that."
Trump expressed grudging admiration. "She doesn't quit. She doesn't give up. I respect that," he said of Clinton. "I disagree with much of what she is fighting for... but she does fight hard."
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