Hillary Clinton forced Donald Trump onto defense over his temperament, refusal to release his taxes and his past comments about race and women during a fiery debut presidential debate Monday—a potentially pivotal moment in a tight election campaign.

Clinton, who has seen her dominance of the presidential race fade in the weeks since the Democratic convention, delivered a strong performance in which she demonstrated a command of policy and a sense of humor, smiling through some of Trump’s strongest attacks. She delivered the best zinger of the night in response to criticism from Trump for staying off the campaign trail recently.

Not only did it have more viewers than any other network showing the debate, but Nightly News anchor Lester Holt’s reviews as moderator were more positive than Matt Lauer received for his interviews with the candidates at a national security forum earlier this month, or CNBC anchors when they did a GOP debate last fall.

Watching the debate was nerve-wracking for NBC Universal chief executive Steve Burke because of the pressure on Holt. Burke said at an appearance in London on Tuesday that Holt “ended up doing a very good job.”

Some Republicans were unhappy with Holt, suggesting that he was unfair because he asked tougher questions of Trump, and challenged his facts on issues like Trump’s support for the war in Iraq and a court case involving the ‘stop-and-frisk’ method of policing.

“I think Donald just criticized me for preparing for this debate,” she said. “And yes, I did. And you know what else I prepared for? I prepared to be president. And that is a good thing.”

Trump came out swinging at the beginning of the debate, and made some effective points on the economy and jobs—some of the aspects of his outsider presidential campaign that have struck a chord with many Americans. But the debate highlighted Trump’s tendency to make false claims as he made inaccurate statements on everything from laws regarding policing, his support for the Iraq War and his contention that Clinton was behind the so-called ‘birther’ conspiracy.

Clinton also hit Trump over his refusal to release his tax returns.

“Why won’t he release his tax returns?” Clinton asked.

“Maybe he is not as rich as he says he is. 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.”

Appearing in the ‘spin room’ after the debate to talk to journalists, Trump said he was happy with his performance.

The showdown between Hillary Clinton and Donald Trump was the most-watched presidential debate ever, with 84 million viewers.

Candidates have rigorously prepared for weeks, but as history has proven, winning is based on conduct. The candidate who proves to be the most poised, precise, and pragmatic will take home the winner’s card.

Clinton has some bragging rights at home. The audience for her first presidential debate was more than double what her husband, former President Bill Clinton, received for his last presidential debate in 1996 (36.3 million viewers).

The second of three scheduled debates will be Oct. 9. The ‘town hall’-style forum will be moderated by CNN’s Anderson Cooper and ABC News’ Martha Raddatz in St. Louis.