Foreign policy and the economy dominated the debate as US Vice President Joe Biden faced off with his Republican rival Paul Ryan on Thursday.
Biden, 69, and Ryan, nearly 30 years his junior, clashed sharply on Iran, the killing of the US ambassador to Libya, and top domestic issues including health care and tax policy during a combative evening in Kentucky.
Biden's fiery performance might be what President Barack Obama needs to widen his lead in the upcoming elections.
Political analyst Bill Schneider told Al Jazeera "Biden really took the fight to Paul Ryan".
"Joe Biden won, I think," said Schneider, adding that Obama would have to measure up to Biden's deft rhetoric in future debates.
Passionate, adamant and frequently laughing, Biden was on a mission to reverse Republican nominee Mitt Romney's polling surge, following his clear victory over Obama in their debate in Denver ahead of the November 6 election.
Biden came under intense pressure from Ryan on the Obama administration's handling of the crisis sparked by the killing of the US ambassador to Libya, Chris Stevens, in Benghazi on September 11.
"We will find and bring to justice the men who did this. Whatever mistakes were made, will not be made again," a steely Biden vowed, and then swiftly went on offence, touting Obama's record on national security.
Biden highlighted Obama's honoured promise to end the war in Iraq, his effort to bring troops home from Afghanistan by 2014, and his decision to make the operation to hunt and kill Osama bin Laden a top priority.
"The president of the United States has led with a steady hand and clear vision. Governor [Mitt] Romney, the opposite," he charged.
Ryan, 42, replied with a fierce assault on Obama's foreign policy record, and complained that the US ambassador to Paris had a Marine detachment while Stevens, in restive Libya, did not.
The Wisconsin congressman also charged that the death of Stevens was symptomatic of a wider problem in Obama's foreign policy, which Republicans charge is purely based on an apologetic stance to US enemies abroad.
Biden replied: "With all due respect, that's a bunch of malarkey."
With Iran's nuclear drive casting a shadow over America's immediate foreign policy, Biden said that Tehran was still a "good way away" from getting an atomic bomb, and vowed it would never get there.
He also accused Romney and Ryan of talking tough on Iran in a way that endangered US security.
"Facts matter. All this loose talk about all they have to do is get to enrich uranium and they have a weapon. Not true. Not true," he said.
Ryan, however, claimed Obama had been asleep at the switch.
"Let's just look at this from the view of the Ayatollahs," he said."What do they see? They see this administration trying to water down sanctions in Congress for over two years. They're moving faster toward a nuclear weapon. They're spinning the centrifuges faster."
Ryan defended Romney's secretly recorded video condemning the "47 per cent" of the electorate that he said was dependent on government and considered themselves victims, calling it a mistake.
Ryan, a seven-term congressman and chairman of the House of Representatives Budget Committee, is popular with conservatives for a budget plan that would slash government spending and create a "voucher" system for the popular
Medicare healthcare programme for seniors.
Democrats say it would leave some retirees paying more of their medical costs.
"We will not be part of any voucher plan, or the privatisation of Social Security," said Biden.
Formerly the chairman of the Senate Foreign Relations and Judiciary committees, Biden was clearly ready to point out the lack of international experience on the Romney-Ryan ticket.
Al Jazeera's Alan Fisher, reporting from Danville, Kentucky, described the debate as "90 minutes of fireworks", especially when it came to the economy.
"Joe Biden says they inherited what he called 'a great recession', but Paul Ryan made the point that this is not what a recovery looks like, with 23 million people in the United States still looking for work," said Fisher.
Ryan said that the US economy is "barely limping along; it's growing at 1.3 per cent...we need real reforms for real reforms for real recovery and that's exactly what Mitt Romney and I are proposing".
The five-point Romney-Ryan plan is essentially an austerity plan, said William Black, an economist from the University of Missouri.
"Ryan said that we need to grow the economy, except that the plan would be austerity, which would stop growth and throw you into recession," he told Al Jazeera.
Obama said Thursday he "could not be prouder" of Biden after the debate.
In an unusual statement, delivered under the wing of Air Force One, Obama said he especially appreciated Biden's strong defence of the middle class in the debate.
The president had gone on the offence earlier in the day, apparently prodded into action by a universally critical response to his debate with Romney in Denver.
"He's trying to go through an extreme makeover," Obama said of his rival on a campaign swing through Florida.
"After running for more than a year in which he called himself severely conservative, Mitt Romney's trying to convince you that he was severely kidding."
Obama's passionate attack fleshed out a new theme adopted by his campaign, namely that Romney, after running to the right to win the Republican nomination, is covering up hardcore conservative stands to win over moderates.
New polling data added to the impression that Romney's polling surge had lifted the Republican ticket into at least a tie less than a month before election day.
Thursday's clash between Biden and Ryan served as a warm-up act for the final two bouts between Obama and Romney, in New York state on October 16 and in Florida on October 22.