US President Barack Obama and Republican Mitt Romney have clashed sharply over their economic plans in the first of three televised debates.
Over 90 minutes, the men jousted over their positions on taxes, healthcare reform and the role of government.
Mr Romney said his rival favoured "trickle-down government" while the president said Mr Romney would "double down" on Bush-era economic policies.
Mr Obama has opened up a narrow lead in the race over the past month.
The president is ahead of Mr Romney in national polls and in many recent polls conducted in the swing states that will decide the election.
The debate was seen as a crucial chance for Mr Romney to regain momentum after a series of tough weeks on the campaign trail.
"The president has a view very similar to the one he had when he ran for office four years ago, that spending more, taxing more, regulating more - if you will, trickle-down government - would work," Mr Romney said.
"That's not the right answer for America."
Mr Romney pledged not to reduce taxes for wealthy Americans, and said Mr Obama had misrepresented his tax plans on the campaign trail.
He hit out at the president for failing to cut the budget deficit in half as he pledged in 2008, and insisted that the US must not allow itself to go down the path of Greece or Spain.
Clashing repeatedly with moderator Jim Lehrer over the time clock, Mr Romney said that in order to reduce the US budget deficit he would repeal Mr Obama's 2010 healthcare law and cut subsidies to US public television, among other unspecified programmes.
And Mr Romney assailed Mr Obama over his plans to eliminate overseas tax breaks, telling him he had "picked losers" by funnelling money into failing companies.
Romney plan 'unbalanced'
Mr Obama deflected criticism of his fiscal management, highlighting Mr Romney's primary-season pledge not to raise taxes.
The president characterised Mr Romney's approach to deficit reduction as "unbalanced".
"There has to be revenue in addition to cuts," Mr Obama said, calling for an end to "corporate welfare" tax breaks for oil companies and corporate jets.
"If you think by closing loopholes and deductions for the well-to-do somehow you will not end up picking up the tab, then Governor Romney's plan may work for you," he said.
"But I think math, common sense, and our history, shows us that's not a recipe for job growth."
With Mr Lehrer, the moderator, occasionally failing to stop the candidates sparring over details, the two men eventually agreed to disagree over the future of Medicare, the government healthcare scheme for over-65s.
Also on healthcare, Mr Romney said that Mr Obama's "Obamacare" reform law of 2010 had increased health costs and kept small businesses from hiring.
He questioned why the president had spent so much time and political energy pushing that reform early in his tenure rather than repairing the economy and creating jobs. And he noted the law passed with no Republican support.
But Mr Romney reprised disputed claims that the president's law cut $716bn from Medicare.
"I want to take that $716bn you've cut and put it back into patients," he said.
Yet Mr Romney praised and defended a plan he himself had previously signed as governor of Massachusetts that is widely hailed as the model for Mr Obama's law.
Mr Obama, meanwhile, said he had been moved to push for the law by stories of voters' healthcare woes and that his plan had kept insurance companies from cutting off coverage from sick people.
"This was a bipartisan idea, in fact this was a Republican idea," Mr Obama said, adding he was now proud of the once-derisive nickname "Obamacare".
Mr Romney was animated, in command of his information, overriding the moderator and interrupting the president, says BBC North America editor Mark Mardell.
On the other hand, President Obama started out looking nervous, and although he warmed up and found his stride he gave long, mini-lectures rather than engaging and arguing, our correspondent says.
Wednesday's debate at the University of Denver was the first time voters across the US had the chance to see Mr Obama and Mr Romney on stage together.
Despite the long presidential campaign, the pair are virtual strangers and have met just three or four times in the past.
Mr Romney's campaign message is that Mr Obama's stewardship of the US economy has been a dismal failure. He points to an enduringly high unemployment rate (currently 8.1%) and poor job growth, and says his experience in business will turn the US economy around.
Mr Obama, by contrast, says his opponent offers little except a rehashing of the "failed" Republican policies that caused the economic crash of 2008.
The president proposes tax rises for the wealthiest Americans to help reduce the federal budget deficit, and says his opponent's plans would hurt the middle class.
But critics say neither man has fully fleshed out his economic policies, and doubts remains about how either Republican or Democrat would tackle the $15tn (£9.3tn) US debt.