Hillary Clinton slated Donald Trump for keeping his personal tax returns and business dealings secret from voters, in a combative opening presidential debate.
The tycoon hit back by repeatedly casting Clinton as a "typical politician" as he sought to capitalise on Americans' frustration with Washington.
The presidential rivals, who are locked in an exceedingly close White House race, argued for 90 minutes over their vastly different visions for the nation's future.
Clinton called for lower taxes for the middle class, while Trump focused more on renegotiating trade deals that he said have caused companies to move jobs out of the US.
The Republican backed the controversial "stop-and-frisk policing" tactic as a way to bring down crime, while the Democrat said the policy was unconstitutional and ineffective.
The debate was confrontational from the start, with Trump frequently trying to interrupt Clinton and speaking over her answers. Clinton was more measured and restrained, but also needled the sometimes thin-skinned Trump over his business record and wealth.
"There's something he's hiding," she declared, scoffing at his repeated contentions that he will not release his tax returns because he is being audited. Tax experts have said an audit is no barrier to making his records public.
Clinton said one reason Trump has refused is that he may well have paid nothing in federal taxes. He interrupted to say: "That makes me smart."
Trump aggressively tried to turn the transparency questions around on Clinton, saying he would release his tax information when she produces more than 30,000 emails that were deleted from the personal internet server she used as US secretary of state.