Republican candidate Mitt Romney (L) with President Barack Obama after the debate
US Republican candidate Mitt Romney won the first of three televised debates with President Barack Obama, polls and analysts say.
After the 90-minute duel centring on taxes, the deficit and healthcare, polls gave omney a 46-67% margin with Obama trailing with 22-25%.
Commentators said Romney appeared in command while Obama was hesitant.
Obama has led national polls and surveys in the swing states that will decide the November 6 election.
The BBC's Mark Mardell says if the gap narrows or Mitt Romney starts moving ahead of Obama, that will be a huge boost for his campaign, and suggest he could win the White House.
However if they hardly budge, then the Republican challenger will be in deep trouble, the North America editor adds.
President Obama appeared hesitant, occasionally asking moderator Jim Lehrer, of US public television network PBS, for time to finish his points.
The two candidates attacked each other's economic plans, with Obama describing his rival's approach as "top-down economics" and a retread of Bush-era policies.
"If you think by closing [tax] 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."
Romney derided Obama's policies as "trickle-down government".
"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," Romney said.
"That's not the right answer for America."
Romney pledged not to reduce taxes for wealthy Americans, and said Obama had misrepresented Romney's tax plans on the campaign trail.
Both camps rushed to defend the respective performances.
"The average person at home saw a president who you could trust," Obama adviser David Plouffe told reporters. "That's what the American people are looking for."
But senior Romney aide Eric Fehrnstrom said the president had spoken "only in platitudes".
"If this were a boxing match, it would have been called by the referee," he said.
Commentators largely agreed that Mitt Romney had performed better.
New York Times columnist and Nobel laureate Paul Krugman said, Obama "did a terrible job in the debate, and Romney did well".
"But in the end, this isn't or shouldn't be about theatre criticism, it should be about substance," Krugman said defending Obama's statements whilst charging that "much of what Romney said was either outright false or so misleading as to be the moral equivalent of a lie".
ABC News quoted one of its consultants and Democratic strategist Donna Brazile as saying: "Mitt Romney did a lot of good... was a little more aggressive than the president."
Washington Post conservative columnist George Will said Romney's performance had "stopped [his slump in the polls] in its tracks".
A CNN/ORC International poll of 430 people who watched the debate showed 67% thought Romney won, compared with 25% for Obama.
A CBS News poll found a 46% support for Romney, 22% for Obama and 32% saying it was a tie.
And a Google survey gave Romney a 47.8% advantage against 25.4% for Obama.
The University of Denver debate was the first in a series of three presidential forums and one vice-presidential encounter this month.
Running-mates Joe Biden and Paul Ryan will meet in Danville, Kentucky on 11 October, before the second presidential debate on 16 October.