The president, looking restrained and at times displeased, did not seize opportunities to attack the Republican challenger on his business record at Bain Capital, the "47 percent" video and his refusal to release more income tax returns.

That enabled Romney to stay on the offensive throughout the two men's first head-to-head meeting in the campaign for the November 6 election.

Democrats tried to put a brave face on Obama's muted appearance. They acknowledged the former Massachusetts governor had scored "style points" but criticized him on substance.

"Governor Romney came to give a performance and he gave a good performance and we will give him credit for that. The problem with it is that none of it was rooted in fact," Obama campaign adviser David Axelrod told reporters.

The engaged and forceful showing from a candidate often criticized as wooden and out of touch delivered a jolt of energy into Romney's flagging campaign that might cut into Obama's slim but steady lead in opinion polls.

Analysts said they still favored the Democratic president's re-election chances.

"Nobody is going to switch sides on the basis of this debate," said Samuel Popkin, a political science professor at the University of California at San Diego.

Axelrod accused Romney of repeated factual errors, such as insisting Obama would cut $716 billion from Medicare, and of changing positions on important issues.

"Again and again and again, he told a story to the American people that is completely in contrast with what he said before and unfounded in fact. And that's going to catch up with him," Axelrod told MSNBC's "Morning Joe."

In Europe, where leaders and finance officials have worked closely with the Obama administration over the past 2 1/2 years to resolve the euro debt crisis, there was consternation at Romney's singling out of deficit-ridden Spain as a poorly administered economy.

"Romney is making analogies that aren't based on reality," Foreign Affairs Minister Jose Manuel Garcia-Margallo said after a meeting of his center-right party.

France's Le Monde newspaper appeared surprised by Obama's sub-par performance. "Where did the favorite go?" it asked on its front page.

Romney's support of the coal industry during the debate sent coal company stocks higher on Thursday. The Dow Jones coal index was 5.05 percent higher.

RIGHT BACK ONTO THE TRAIL

The candidates were jumping right back onto the campaign trail on Thursday with rallies in Colorado, Wisconsin and Virginia, three of the closely contested states where the election is likely to be decided.

"For now we'll chalk this up as a wake-up call for the president, who still has a vastly superior campaign organization and owns the pivotal issue of Medicare," Greg Valliere, chief political analyst at Potomac Research Group, wrote in a note to clients on Thursday morning.

"But this is still a winnable election for Romney and that was the ultimate take-away last night," he said.

Within hours of the debate, Republicans launched a string of new ads hoping to capitalize on Romney's momentum. One had him presenting his plan for creating 12 million new jobs. Another, aired in Wisconsin by the Super PAC Restore Our Future, called on voters to demand better than Obama's "new normal" economy.

The Republican National Committee compiled a web video that zoomed in on Obama smirking during the debate as Romney jabbed him on healthcare and economic policies.

Going into the debate, Obama held a lead of 5 to 6 percentage points over Romney in most national polls, and is ahead by at least narrow margins in almost all the battleground states where the election will be decided.

He was up by 6 points among likely voters in Wednesday's Reuters/Ipsos daily tracking poll, leading by 47 percent to Romney's 41 percent, a margin that has held fairly steady since mid-September.

Obama next squares off with Romney on October 16 in Hempstead, New York, in a "town meeting" format during which voters will directly question the candidates. The third and last presidential debate is set for October 22 in Florida.

The only vice presidential debate, between Vice President Joe Biden and Ryan, will be next Thursday in Danville, Kentucky.

WHAT WASN'T SAID

Even Democratic pundits sharply criticized Obama for looking grim on the stage, giving answers that were meandering and professorial and, most of all, for not hitting back.

Obama steered clear of attacks that helped build his lead, most startlingly by not uttering the phrase that has dominated the campaign for much of the past two weeks: "47 percent.

That would be the percentage of Americans who Romney - speaking at a private fundraiser that was secretly videotaped in May - said were "victims" dependent upon government and unwilling to take responsibility for their own lives.

Obama did not challenge Romney for adopting a more moderate tone, which would appeal to centrist voters, than the strongly conservative line he has toed in the campaign.

And he also never mentioned Romney's private equity firm, Bain Capital. The Obama campaign had spent months portraying Romney as a job-killer, saying his firm shut down companies, triggered layoffs and helped send thousands of jobs overseas.

Romney zeroed in on weak economic growth and 8.1 percent unemployment that have left Obama vulnerable in his effort to win a second four-year term. The monthly unemployment for September, due on Friday, could be another setback for Obama.

Government has taken on too big a role under Obama, dampening job creation, Romney argued.

Obama said his leadership had brought the economy back from the brink, with 5 million jobs created in the private sector, a resurgent auto industry and housing beginning to rise.