U.S. President Barack Obama's campaign is promising "adjustments" in its message after Republican presidential candidate Mitt Romney took an aggressive stance in the first debate, appearing to get the upper hand in his bid to gain momentum ahead of next month's election.

A number of analysts, and political pundits from both sides of the aisle, seemed to give the night to Romney, calling it his best debate performance since the end of the Republican primaries.

According to a CNN/ORC international poll taken after the debate, 67 per cent thought Romney won, compared to 25 per cent for Obama.

"This is going to be a test of how much debates can change the polls. There's no real question that Romney won the first debate," Larry Sabato, director of the University of Virginia Center for Politics," said in an email to CBC News.

"Obama left his A game at the White House, that's for sure. Most Democrats are complaining bitterly on Twitter about how many opportunities Obama missed. But it was a wonky debate, not scintillating," he said.

"Will the debate matter? Are the partisans just cheering for their side? We'll find out."

Obama campaign strategist David Axelrod told reporters that the president is "eager" for the next debate. "I'm sure that we will make adjustments," Axelrod said.

'Manhandled the president'

Tom Bevan, co-founder of RealClearPolitics.com, told CBC News that he thought Romney was very strong, made his points effectively without being mean-spirited and "manhandled the president for the first 30 minutes."

The debate, held at the University of Denver and moderated by PBS's Jim Lehrer, was expected to attract at least 50 million viewers.

A panel of experts on CNN all seemed to agree that Romney came out on top. Democratic strategist James Carville said it looked like "Romney wanted to be there and Obama didn't."

Senior political analyst David Gergen said he was surprised by the outcome.

"A week ago people were saying this was over. We've got a horse race. [Romney's] performance was head and shoulders above anything we've seen him do before," Gergen said.

Some described the president's performance as flat, saying he looked perturbed at times during the evening. But not all experts agreed.

David Birdsell, dean of the Baruch College School of Public Affairs in New York, told CBC News that he thought Romney failed to get the job done and "lost control of the clock," adding that Obama was able to drive the agenda.

"In a debate where Mitt Romney really needed to make up significant ground on Barack Obama, he failed to do that," Birdsell said.

The debate, the first of three between Obama and Romney, focused on domestic issues, including taxes, health care and education.

No sharp exchanges, major gaffes

There were no sharp exchanges, no major gaffes and neither candidate took partisan shots. Instead, both focused on policy and threw around many figures and percentages to back up their arguments.

'My priority is putting people back to work in America. They're suffering in this country.'—Republican candidate Mitt Romney

Also, no mention was made of issues that have been central to the Democratic campaign — Romney's time at the private equity firm Bain Capital and his "47 per cent" comments, in which he said that nearly half of Americans consider themselves victims and are dependent on the government.

Instead, Romney went on the offensive, hammering Obama on his economic record and accusing the president of putting too much faith in the state with his "trickle-down government" approach to the economy.

"My priority is putting people back to work in America. They're suffering in this country. And we talk about evidence — look at the evidence of the last four years. It's absolutely extraordinary. We've got 23 million people out of work or stopped looking for work in this country," Romney said.

The Republican candidate said middle-income Americans are "just being crushed" under the president's policies and that Obama's re-election will continue a "middle-class squeeze" with incomes going down, prices going up and chronic unemployment.

Romney slammed Obama for saying he'd cut the deficit in half but instead doubling it.

'Trillion-dollar deficits'

"Trillion-dollar deficits for the last four years. The president's put in place as much public debt, almost as much debt held by the public as all prior presidents combined."

He said he'd repeal Obama's health care plan and chastised the president for focusing on that issue during his four-year term, instead of the economy.

"I just don't know how the president could have come into office facing 23 million people out or work, rising unemployment and economic crisis at the kitchen table and spend his energy and passion for two years fighting for Obamacare instead of fighting for jobs for the American people," Romney said.

Republican presidential nominee Mitt Romney and U.S. President Barack Obama sparred in Colorado on Wednesday night during the first of three debates. (Charlie Neibergall/Associated Press)

Obama went after Romney's tax plan, saying it calls for a $5-trillion tax cut, $2 trillion in additional military spending and an extra $1 trillion in lost government revenue by extending the Bush-era tax cuts.

"How we pay for that, reduce the deficit, and make the investments that we need to make, without dumping those costs onto middle-class Americans, I think is one of the central questions of this campaign."

Romney shot back that he did not have a $5 trillion tax cut as part of his plan and that none of his tax cuts would add to the deficit.

'It's math. It's arithmetic'

But Obama was undeterred: "For 18 months he's been running on this tax plan. And now, five weeks before the election, he's saying that his big, bold idea is 'never mind.' And the fact is that if you are lowering the rates the way you describe, governor, then it is not possible to come up with enough deductions and loopholes that only affect high-income individuals to avoid either raising the deficit or burdening the middle class. It's — it's math. It's arithmetic."

'It's estimated that by repealing Obamacare, you're looking at 50 million people losing health insurance at a time when it's vitally important.'—U.S. President Barack Obama

Obama also defended his record on the deficit saying he entered the office with "a trillion dollar deficit greeting me" and that he "had to take some initial emergency measures to make sure we didn't slip into a Great Depression."

On health care, Obama said his plan brings down costs and is based on the model Romney set up as governor of Massachusetts. He said that while Romney plans to repeal it, he has given no details on what he'd replace it with.

"It's estimated that by repealing Obamacare, you're looking at 50 million people losing health insurance at a time when it's vitally important," the president said.

Obama also challenged Romney on his plan to repeal and replace regulations passed after the 2008 financial crisis.

"Does anyone think there is too much oversight and regulation of Wall Street? Because if you do, then Governor Romney is your candidate," Obama said.

"And at some point, I think the American people have to ask themselves is the reason that Governor Romney is keeping all these plans to replace secret because they're too good?"

The next two debates are Oct. 16 in New York and Oct. 22 in Florida.

Vice-President Joe Biden and Romney's running mate, congressman Paul Ryan, have one debate in Kentucky on Oct. 11.

With files from The Associated Press