WASHINGTON - Joe Biden's spirited performance in the vice presidential debate had Republicans criticizing him on Friday for snide grins and a comment on Libya, but it set the stage for President Barack Obama to try to regain his footing in a rematch with challenger Mitt Romney next Tuesday.

After Obama was seen as largely passive against resurgent Republican Romney last week in their first debate before the Nov 6 US election, Vice-President Biden fired up Democrats in Thursday night's debate by aggressively challenging Paul Ryan, Romney's running mate, on taxes, healthcare and foreign policy.

A Reuters/Ipsos poll conducted after the debate showed that 42 percent of registered voters felt Biden had won, versus 35 percent who picked Ryan. Twenty-three percent said they did not know who had come out ahead.

"Vice presidential debates don't change electoral outcomes, but it may have done a little bit to stem the tide," said Ipsos pollster Julia Clark said.

US Vice-President Joe Biden (L) and Republican vice presidential nominee Paul Ryan shake hands at the conclusion of the vice presidential debate in Danville, Kentucky, Oct 11, 2012. [Photo/Agencies]

In a sign the race is tightening again, Romney led Obama by 1 percentage point, 46 to 45 percent, among likely voters in the Reuters/Ipsos daily online tracking poll released on Friday. Romney led by 3 percentage points in Thursday's poll. Most poll respondents were questioned before the vice presidential debate.

More than 51 million Americans watched the vice presidential debate, ratings data released on Friday showed.

Republicans tried to prevent Biden's performance from giving momentum to the Democratic ticket by criticizing the vice-president's demeanor during the debate. They said Biden grinned too much and was rude to Ryan during their animated encounter.

They made Biden's comments about security at the US diplomatic compound in Benghazi, Libya, on September 11 their theme of the day, hoping to puncture Obama's credibility on foreign policy.

When asked in Kentucky about whether the mission had requested more security in the months leading up to the attack, Biden said, "Well, we weren't told they wanted more security again. We did not know they wanted more security again."

At a campaign rally in Richmond, Virginia, Romney accused Biden of contradicting testimony by US State Department officials who said this week the consulate had raised fears about security before the attack, which killed Ambassador Christopher Stevens and three other Americans.

"He's doubling down on denial," the former Massachusetts governor told a cheering crowd.

Romney and Ryan met Friday evening for a rally in Lancaster, Ohio, where Romney praised his running mate's performance - at one point referring to him as "this great vice president."

"There was one person on the stage with the thoughtfulness, who was respectful, who was steady and poised," Romney said. "There was one person on that stage you'd want to be with if they were in a crisis, and it's this man right here."

Democrats dismissed the Republicans' stance as a bid to politicize a tragedy.

Biden sought to keep up the pressure on the Republican ticket on Friday, using a visit to Ryan's home state of Wisconsin to blast him for his positions on abortion and the war in Afghanistan.

"If anyone had a doubt about what's at stake in this election when it comes to women's rights and the Supreme Court, I'm sure they were settled last night," Biden told a rally.

Biden believes abortion should be legal. Ryan opposes it except in cases of rape, incest or a threat to a mother's life.