Clinton poked, prodded and quoted Trump's own words, goading the famously thin-skinned Republican nominee. Trump took the bait, repeatedly interrupting angrily or dismissively throughout the night.
He couldn't resist attacks, even when it was obvious they would backfire -- such as his criticism of Clinton for dropping off the campaign trail ahead of the debate to prepare.
"Yes, I did. And you know what else I prepared for?" Clinton shot back. "I prepared to be president."
Here are six takeaways from the first presidential debate:
Trump takes the bait
Trump is the self-proclaimed counterpuncher, but it was Clinton whose restraint was on display: She waited for Trump to create an opening before she pounced.
She let moderator Lester Holt grill Trump about his refusal to release tax returns before delivering her own withering assessment of his insistence that a "routine audit" be completed first.
"Maybe he is not as rich as he says he is," Clinton said. "Maybe he is not as charitable as he claims to be... Maybe he doesn't want the American people to know that he has paid nothing in federal taxes."
"There is something he is hiding," she said.
Trump lost his cool -- at a cost. He came close to admitting that he didn't pay federal taxes, saying that "makes me smart" and that the money "would be squandered" anyway.
At another point, he insisted his refusal to pay contractors who'd done work for his businesses was smart.
"I'm certainly relieved that my late father never did business with you," Clinton said.
Trump, meanwhile, paid the price for his decision to wing it.
Unlike the GOP primary debates, where Trump would often disappear while other candidates bickered, only to interject with a zinger, he had no other candidates or aggressive moderators to save him -- and it showed.
Despite opportunities to do so, he never hit Clinton on the 2012 Benghazi attacks or Clinton Foundation donors' access to the State Department, and he only briefly mentioned her use of a private email server. All three attacks -- elevated by Trump himself at his rallies -- are at the core of the GOP case that Clinton is untrustworthy.
Trump's pitch to blue-collar voters
Trump's brightest spots came early in the debate, when he invoked Clinton's 2012 praise of the Trans-Pacific Partnership as the "gold standard" of trade deals. (Clinton now opposes the deal.)
"You were totally in favor of it," Trump said. "Then you heard what I was saying, how bad it is, and you said, 'I can't win that debate.'"
It was part of a theme he worked hard to drive in the debate's early stages: Clinton, he said, has been in Washington for nearly 30 years, and has done little to improve economic conditions for Americans -- a message that could resonate in manufacturing-heavy states like Ohio and Pennsylvania that are crucial to Trump's electoral math.
Attacking Clinton's comments on solar energy powering "new economic activity," Trump said: "You've been doing this for 30 years. Why are you just thinking about these solutions right now? For 30 years, you've been doing it, and now you're just starting to think of solutions."
After a barrage of Trump attacks, Clinton sarcastically said, "I have a feeling that by, the end of this evening, I'm going to be blamed for everything that's ever happened."
Trump shot back: "Why not?"
Trump's strained relationship with the truth
Trump lied repeatedly Monday night -- including some real whoppers.
When Clinton claimed Trump "thinks that climate change is a hoax perpetrated by the Chinese," Trump shot back: "I do not say that. I do not say that."
Of course, Trump did say that. On November 6, 2012, Trump tweeted, "The concept of global warming was created by and for the Chinese in order to make U.S. manufacturing non-competitive." It became the most-retweeted item on Twitter during the debate.
He called Holt's factual citation of a 2002 interview in which Trump endorsed the war in Iraq "wrong, wrong, wrong," as fact-checkers disagreed.
He falsely blamed Clinton for birtherism. He said murder rates in New York City are climbing, when they are on the decline. And he said Clinton had been fighting ISIS "her entire adult life." Clinton was born in 1947; ISIS only formed in the mid-2000s.
"I hope the fact-checkers are turning up the volume," Clinton said at one point.
Clinton calls Trump's behavior racist
Trump said he knew he'd face questions about his five-year history of birtherism.
Yet he had no new answers to offer. When Holt asked why Trump decided to finally acknowledge that President Barack Obama was born in the US, Trump said it was because he wanted to change the topic.
"I want to get on to defeating ISIS, because I want to get on to creating jobs, because I want to get on to having a strong border, because I want to get on to things that are very important to me and that are very important to the country," he said.
While falsely blaming Clinton's 2008 presidential campaign for the questions about Obama's birth, Trump also took credit for bringing up the non-issue in the first place. "I was the one that got him to produce the birth certificate," he said. "And I think I did a good job."
Clinton responded by turning the spotlight back on her GOP foe.
"Well, just listen to what you heard," Clinton said.
She pointed to the 1970s Justice Department lawsuits that Trump faced over accusations of racial discrimination in housing properties he owned.
"He has a long record of engaging in racist behavior," Clinton said. "And the birther lie was a very hurtful one."
Trump's misplaced aggression
Trump has long polled better with men than women -- and that gap could grow after Monday night's debate.
He interrupted Clinton dozens of times, and talked over Holt when he tried to interject. He blasted Clinton's "stamina." And when Clinton attacked Trump over his remarks about women, Trump proved her point by digging in against an old foe.
"Rosie O'Donnell, I said very tough things to her, and I think everybody would agree that she deserves it and nobody feels sorry for her," Trump said.
He zealously defended himself, but didn't attack Clinton with the same gusto. And because of it, Clinton was able to easily move past potential problem areas.
Asked about her use of a private email server during her tenure at the State Department, Clinton gave a shorter, simpler answer than she has before. "I'm not going to make any excuses, it was a mistake," she said.
Trump shot back that it was "more than a mistake. That was done purposely." But then he dropped the topic.
Later, he briefly came back to it, saying he'd release his tax returns "against my lawyers' wishes," under one condition: "I will release them as soon as she releases her 33,000 emails."
The crowd cheered, violating Holt's admonition to keep silent. And then, again, Trump moved on -- never mentioning that James Comey, the FBI director, also harshly criticized Clinton's email practices, and never again returning to the topic.
They really don't like each other...
...And it shows. With two debates to go, this is going to get nastier.
A preview of what's in store came at the end, when Clinton -- attacking Trump's treatment of women -- called him "a man who has called women pigs, slobs and dogs."
She said he'd referred to a Latina beauty contestant as "Miss Piggy. Then he called her Miss Housekeeping."
An agitated Trump twice asked, "Where did you find this?"
The woman, 1996 Miss Universe Alicia Machado of Venezuela, told The New York Times and "Inside Edition" this year that Trump repeatedly mocked her weight.
Trump went into the spin room after the debate -- a move unheard of at general election debates - and credited himself with not taking a shot at Bill Clinton's extramarital affairs.
He told Fox News conservative host and Trump supporter Sean Hannity afterward that it seemed inappropriate with Bill and Chelsea Clinton in the front row -- but implied he might in the future.
For Clinton's campaign, the challenge will be turning a debate-night victory into sustained success -- pressing the same themes in the days ahead as she attempts to reverse Trump's climb in national and battleground state polls.
Trump will have to wait until Oct. 9 for another shot at Clinton.