Romney now leads the Democrat by 47 percent to 44 percent among likely voters in the online poll, with less than a month before the November 6 election. The Republican had a one-point lead over Obama in survey results on Wednesday, his first in more than a month.

Romney has been enjoying one of his best runs of the campaign after handily winning the first presidential debate last week, partially due to Obama's passive performance in that contest.

"The momentum is in Romney's direction right now," Ipsos pollster Julia Clark said.

Vice President Joe Biden will look to recover some momentum for Obama's re-election bid when he faces off Thursday evening with Republican challenger Paul Ryan in the only vice presidential debate of the campaign.

The veteran Biden, an accomplished debater known for delivering withering attacks with a smile, will try to improve the outlook for the Democrats before Romney and Obama meet for a second debate Tuesday.

Ryan, chairman of the House of Representatives budget committee, will look to ward off aggressive moves from Biden while avoiding his own tendency to get mired in numbers.

Clark said Romney's rise in the poll comes from convincing undecided voters, not winning over Obama supporters. And there were signs that a large number of votes are still up for grabs.

Sixteen percent of registered voters said they could still change their minds about whom to vote for, including 28 percent of independents surveyed.

Seven percent of registered voters said they had already taken advantage of programs that allowed them to cast their ballots early, and an additional 27 percent said they planned to vote before Election Day.

The online survey of 1,092 likely voters and 1,312 registered voters was conducted between October 7 and 11. The precision of the Reuters/Ipsos online polls is measured using a credibility interval. In this case, the poll has a credibility interval of plus or minus 3.1 percentage points for registered voters and 3.4 for likely voters.