From the debate's outset, a forceful Obama took dead aim at Romney's inconsistencies on foreign policy, frequently accusing the Republican of veering "all over the map" in his stances on Iran, Iraq, Libya and the Arab Spring.
Just a few minutes into their showdown in Boca Raton, Fla., the president pounced, noting that his rival for the White House once said Russia was America's biggest geopolitical foe, called for troops to remain in Iraq and asserted that America "should not move heaven and Earth" to capture one man — 9-11 mastermind Osama bin Laden.
"The 1980s are calling and asking for their foreign policy back," Obama said at one point to Romney, who took far more centrist, moderate stands on conflicts in the Middle East on Monday than he has previously on the campaign trail.
"Governor, when it comes to our foreign policy you seem to want the policies of the 1980s, just like you want to import the social policies of the 1950s and the economic policies in the 1920s."
As they sat in close physical proximity at a semi-circular table across from debate moderator Bob Schieffer of CBS News, the president also reminded prime-time viewers of Romney's support of George W. Bush's record.
"He's praised George Bush as a good economic steward and Dick Cheney as somebody who shows great wisdom and judgment — and taking us back to those kinds of strategies that got us into this mess is not … going to maintain leadership and take us into the 21st century," he said.
In another verbal barb, Obama assailed Romney's budget plan for including "military spending that our military is not asking for."
When he noted that Romney has complained that the U.S. Navy now has fewer ships than it did decades ago, Obama delivered his most cutting, insulting jab of the night.
"We also have fewer horses and bayonets," he said. "We have these things called aircraft carriers, where planes land on them; we have these ships that go underwater — nuclear submarines .… It's not a game of Battleship."
Romney, for his part, displayed a far less aggressive demeanour in the final presidential faceoff than he did last week in Hempstead, N.Y., during Debate No. 2. He had no reply to Obama's Battleship remark, for example.
Indeed, Romney was on the defensive for at least the first half of the 90-minute clash to the extent that he occasionally agreed with Obama on various foreign policy stances. In particular, Romney said he backed Obama's plan to pull American troops out of Afghanistan by the end of 2014.
He'd previously criticized the president for the timeline.
Romney also sat serenely several times as the president ridiculed his past remarks and positions.
And yet even though Obama was largely considered the winner of the final debate, Romney, perhaps, was the ultimate victor following their three prime-time duels.
Obama was comfortably ahead of his rival in the polls prior to their first debate on Oct. 3; Romney has now tied him nationally and is gaining on him in the critical swing states that will determine the Nov. 6 vote.
The Florida showdown was focused on foreign policy, suddenly a key issue as the roller-coaster ride of the election campaign heads into the home stretch.
Nonetheless it often veered into domestic policy, with Obama zinging Romney about shipping jobs overseas as head of Bain Capital and assailing him for once advocating that the U.S. auto industry be allowed to go bankrupt.
Romney, meantime, said America's role is "to make the world more peaceful" before taking a shot at Obama on the economy.
"America must be strong. America must lead. For that to happen, we have to strengthen our economy here at home. You can't have 23 million people struggling to get a job. You can't have an economy that over the last three years keeps slowing down its growth rate," he said.
He also scored the odd foreign policy point of his own while managing not to commit any major gaffes.
Iran is "four years closer" to having a nuclear weapon for potential use against Israel, Romney said repeatedly, laying the blame on the Obama administration for being too soft on the regime.
"The president began what I have called an apology tour of going to various nations in the Middle East and criticizing America," Romney said. "All of these things suggested, I think, to the Iranian mullahs that, you know, we can keep on moving along."
But it was his dove-like stances on several issues that were most surprising. During a discussion on anti-American sentiment in the Middle East, Romney said America "can't kill our way out of this mess."
"We have to help these nations build civil societies," said Romney, who has previously opposed the U.S. being involved in nation-building.
Foreign policy was largely considered a strong point for Obama with the exception of his administration's recent handling of anti-American violence in Libya.
The president's decision to authorize the raid in Pakistan by U.S. Navy SEALs that resulted in the death of Osama bin Laden has been one of the biggest triumphs of his four years in office.
The Libya situation was considered a significant vulnerability for the president heading into last week's clash. But Romney was widely seen as having fumbled when he accused Obama of waiting two weeks before characterizing the attack on the U.S. consulate in Benghazi last month as an act of terror.
That attack killed four Americans, including Chris Stevens, the U.S. envoy to Libya.
Obama — whose news conference the day after the attack included the phrase, "No acts of terror will ever shake the resolve of this great nation" — was vindicated when moderator Candy Crowley corrected Romney in the midst of his attack.
Romney, perhaps mindful of that bad moment last week, didn't press Obama on Libya on Monday. Instead, the debate focused more on the Arab Spring, Iraq, Israel and China.
Team Obama was confident about their man's prospects leading up to the debate, with senior adviser David Axelrod ridiculing Romney's gaffe-ridden foreign trip in July as a "Dukes of Hazzard tour of international destinations."
Despite the vitriol between the campaigns, however, Obama and the first lady, Michelle Obama, mingled on the stage with Romney, his wife, Ann, and a collection of their children and grandchildren following the debate. They chatted and laughed for about five minutes.
At one point, one of Romney's young grandsons reached out for Obama as the president leaned down to speak to him. A Romney daughter-in-law quickly stepped in to refocus the boy.