Mitt Romney regained momentum in the first debate by aggressively standing up to Barack Obama, analysts said, but it remains to be seen how much he can budge the needle in the White House race.
Obama spoke longer during the 90-minute showdown in Denver on Wednesday, but the Republican challenger landed more blows against an often-subdued president in their first of three debates ahead of the November 6 vote.
"I don't think there's any doubt... that Romney won," G. Terry Madonna, director of the Center for Politics and Public Affairs at Franklin and Marshall College, who has monitored elections since 1960, told AFP.
A flash poll conducted by CNN bore that out: adult viewers of the debate by a 67-25 percent margin said Romney won.
Similarly, a CBS News instant poll had undecided voters proclaiming Romney the victor by a two to one margin.
"The president certainly wasn't on the top of his game tonight," Madonna said.
Romney was more aggressive "without being pugnacious or provocative or combative," hitting the president on his economic record while steadily returning to the theme that a Romney presidency would create more jobs and stimulate faster economic growth than the current administration.
"Was it a huge victory? No. Did the president fall flat on his face? Of course not," Madonna said.
"But what Romney had to do was get up on the stage, be the aggressor, make his points and instill a sense of confidence among Republicans that he can still win an election... and I think he accomplished that."
Romney, a former governor of Massachusetts, is desperate to turn around poll numbers that show him trailing the president going into the home stretch.
From the beginning he challenged Obama on taxes and federal spending, insisting that the president's claim that Romney would bring $5.4 trillion in tax cuts geared towards the wealthy was "inaccurate."
"The president has a view very similar to the view he had when he ran four years ago, that a bigger government, spending more, taxing more, regulating more -- if you will trickle-down government -- would work," Romney said.
"That's not the right answer for America. I'll restore the vitality that gets America working again," he vowed. "Middle-income families are being crushed, and the question is, how to get them going again."
Obama seemed to shy away, adopting a far less confrontational tone than many of the attack ads his campaign has been running.
"He didn't hit Romney very hard. He didn't bring up the 47 percent, for example," said Clyde Wilcox, a government professor at Georgetown University.
Romney has been badly stung in recent weeks after a video emerged showing him disparaging nearly half of Americans who pay no federal income tax, saying they were self-described "victims" who depended on government handouts.
Thomas Mann, a congressional expert at the Brookings Institution think-tank, said Obama's "decision not to go for the jugular on the 47 percent" was a surprise.
"Liberals wanted more blood on the floor and Obama didn't draw it from Romney," he added. "This is beginning to take shape as a Romney win, and I suspect it will gather force."
Romney's own campaign was quick out of the gate claiming the upper hand.
"If this was a boxing match, it would have been called an hour into the fight," boasted Romney political adviser Eric Fehrnstrom.
Even Obama senior strategist David Axelrod acknowledged Romney took the battle to the president.
"What you saw tonight was what we saw during the primaries, which is (that) governor Romney is a very eager and willing candidate on the attack," Axelrod said in Denver.
Analysts expected a one or two percentage point bump for Romney.
"I think that he has still an uphill battle," Wilcox said. "Maybe in two or three days you'll see him ahead in Virginia, maybe in Florida," he added.
But Obama leads in nearly all other battlegrounds, including in Ohio and Wisconsin, and the question is whether Romney can claw his way back in any of those states to give him a realistic chance at winning on November 6.
David Gergen, an advisor to four presidents who served in Republican and Democratic administrations, said Romney's clear debate victory left the campaign wide open.
"We've got a horse race," Gergen said on CNN. "Mitt Romney came prepared to play. He drove the debate."