The foes, drained by fatigue, charged through the swing states that will dictate their fates, taking final shots hours before polls open in an election that will decide whether Obama wins a second White House term.
"We need to have new leadership and new vision for the country," said Romney, the Republican nominee, at his penultimate campaign event in an aircraft hangar in Columbus in the potentially pivotal swing state of Ohio.
"President Obama promised change, but he couldn't deliver it," Romney told thousands of cheering supporters, who chanted "One More Day, One More Day" under a huge banner that read "Victory in Ohio."
Earlier, Romney -- despite trailing in polls of the battleground states that will decide the election -- forecast he would win, and urged supporters in Virginia to help get out the vote on Tuesday.
"We thank you and ask you to stay with it all the way until we win tomorrow (Tuesday) night," Romney said, sparking wild cheers.
The Republican candidate was holding his final rally in New Hampshire, though scheduled get out the vote stops in Ohio and Pennsylvania on election day.
Obama, barnstorming with rock legend Bruce Springsteen and rapper Jay-Z, delivered a similar message in the liberal college town of Madison, Wisconsin, pleading with supporters to stick with him in a final push to the finish.
"If you're willing to work with me again, and knock on some doors with me, make some phone calls for me, turn out for me, we'll win Wisconsin. We'll win this election. We'll finish what we started," he said.
Obama is hoping to defy historic precedents which suggest that presidents who preside over shaky economies and high unemployment fail to win re-election.
Later, the president held his last rally of the campaign in Ohio, and repudiated Romney's claim to be a candidate of change.
"You know that I know what real change looks like because you've seen me fight for it," Obama said.
"I've got the scars to prove it. I've got the gray hair to prove it."
Obama was later to wind up his re-election bid with his last-ever campaign event in Des Moines, Iowa, the city where his unlikely quest for the presidency began in early 2007.
Then, he was headed home to Chicago for election day.
Election eve polls cemented the impression that Obama has the slightest of leads after a campaign that has cost billions of dollars, but cannot take victory, and the historical validation of re-election, for granted.
The final national polls showed an effective tie, with either Romney or Obama favored by a single point in most surveys, reflecting the polarized politics of a deeply divided nation.
Obama however led by three points in national polls conducted by Pew Research and by the Washington Post and ABC News, suggesting that if either candidate could boast of 11th-hour momentum, it was the 44th US president.
His last line of defense in the industrial Midwest also seemed to be holding: Obama led the RealClearPolitics.com average of polls in crucial Ohio by 2.9 percent, and was up by 2.4 points and 4.2 points in Iowa and Wisconsin.
Should those polls be reflected in vote totals on Tuesday, Obama would become only the second Democrat, after Bill Clinton, to win a second four-year term since World War II.
Obama was also up by a narrow margin in swing states Virginia, New Hampshire, Colorado and Nevada while Romney led by similarly thin margins in poll averages of Florida and North Carolina.
Romney's camp insists that the former Massachusetts governor will profit from an anti-Obama wave on Tuesday and contends the polls overstate the proportion of Democrats in the electorate.
Obama's team however, cheered by early vote data and the neighborhood-by-neighborhood political machine the president has assembled, insisted that they would be vindicated by the election.
"We're going to win the electoral vote and we're going to win the popular vote," said Obama's political guru David Axelrod.
"It's going to be a close election as we always said. This is the season for weird theories, but we're very, very confident of both those things."
Springsteen told an 18,000 strong crowd in Wisconsin that his life in music had been dedicated to charting the distance between the American dream and American reality.
"Our vote tomorrow is the one undeniable way we get to determine the distance in that equation," said The Boss, who was traveling with Obama aboard Air Force One.
Obama's campaign deployed former president Bill Clinton to Pennsylvania, ostensibly a safe Democratic state but one which has seen a late run by Romney -- evidence, according to Obama's team, of desperation.
"I'm for President Obama because ... he's got a much better plan for the future," said Clinton, who has overcome acrimony left over from Obama's 2008 primary defeat of his wife Hillary to embrace the president.
Florida, famous for the presidential election debacle 12 years ago which required the hand-counting of thousands of ballots, faced some new election-related problems ahead of Tuesday's vote.
The state's Democratic Party filed a federal lawsuit on Sunday over long delays encountered by some voters who were unable to cast votes in southern Florida despite spending hours in line.