Apparently keen to avenge his boss following Obama's dismal debate performance last week, Biden was fiery and combative, in stark contrast to the president's listless, halting demeanour in Denver.
The vice-president rolled his eyes. He sneered. He laughed disdainfully. He interrupted.
He pushed Ryan for specifics. He mocked Romney's infamous "47 per cent" comments. He accused the Romney-Ryan ticket of constantly switching positions.
He ridiculed their foreign policy stances, particularly Ryan's mid-debate stumble that U.S. troops should remain in eastern Afghanistan, the deadliest region in the country. He called out Ryan for denying established Romney policies, particularly an increase in defence spending.
For most of the debate, Ryan struggled to find solid footing, frequently sipping water as Biden hammered away at him.
The Wisconsin congressman grew more confident towards the end of the night, although he seemingly tried to squeeze as many anti-Obama talking points into the final minutes after failing to effectively do so earlier.
The president rejoiced.
"I'm going to make a special point of saying that I thought Joe Biden was terrific tonight," he told reporters as he returned from a campaign swing in Florida.
"I could not be prouder of him. I thought he made a very strong case. I really think that his passion for making sure that the economy grows for the middle class came through. So I'm very proud of him."
A CBS News snap poll suggested viewers also felt Biden was the clear victor. Fifty per cent said he won, 31 per cent thought Ryan was triumphant and 19 per cent considered it a tie.
The debate started with a question on the crisis in Libya, with Ryan maligning the White House for a flailing narrative over its handling of the anti-American violence that erupted in the Middle East, resulting in the death of the U.S. ambassador to Libya and three other Americans.
"This is becoming more troubling by the day," Ryan said, alleging it took the White House two weeks to describe the attack on the Benghazi consulate a terrorist attack.
Biden fired back.
"With all due respect, that's a bunch of malarkey ... not a single thing he said was accurate," Biden replied.
The vice-president forcefully defended the administration's initial public comments on the Libyan crisis, saying White House officials were guided by the information they were receiving from the intelligence community as the chaos overseas unfolded.
"Whatever mistakes were made will not be made again," he added.
He also noted Obama promised to end the war in Iraq — and did so — and that he made it a top priority to pursue Osama bin Laden, the mastermind behind the Sept. 11, 2001, terrorist attacks.
Romney, on the other hand, once said he wouldn't move heaven and Earth to get the al Qaida kingpin, Biden pointed out, and that U.S. troops should remain in Iraq and Afghanistan.
Laughing contemptuously at times, Biden also attacked Ryan's insistence that Obama's weakness on foreign policy has contributed to Iran's determination to develop a nuclear program for use against Israel.
When Iranians see the White House put daylight between America and Israel, Ryan said, it encourages them to proceed.
"A Romney administration will have credibility on this issue," Ryan said.
"That's incredible," Biden sneered in response.
The men also sparred on tax policy, health-care reform and the economy, with Biden surprisingly strong in all areas.
Biden wasted no time raising Romney's assertions that 47 per cent of Americans were dependent on government handouts, and accused the Michigan-born Republican of opining that the auto industry should have been left to go bankrupt in 2008.
"It shouldn't be surprising for a guy who says 47 per cent of the American people are unwilling to take responsibility for their own lives," he said.
Ryan shot back at the Obama administration for its inability to robustly rejuvenate a sputtering economic recovery.
"Twenty-three million Americans are struggling for work today," he said. "Fifteen per cent of Americans are living in poverty today. This is not what a real recovery looks like."
The hot-button social issue of abortion was also a topic of debate between the two men, both of them Catholics. Biden said he would never force his own religious beliefs on other people, while Ryan spoke of nicknaming his daughter "Bean" after seeing an ultrasound photo of her fetus.
"I do not believe that we have a right to tell other people that, women, that they can't control their body," Biden said. "It's a decision between them and their doctor, in my view, and the Supreme Court. I'm not going to interfere with that."
Ryan stood in stark contrast, accusing Obama of supporting abortion "without restriction and with taxpayer funding."
"I respect people who don't agree with me on this, but the policy of a Romney administration will be to oppose abortion with the exceptions for rape, incest and life of the mother," he said, a change from his previous, even more conservative position on the issue.
Vice-presidential showdowns don't generally generate much buzz or carry high stakes. But amid the rollercoaster ride of the 2012 campaign — and the aftermath of Obama's lacklustre debate performance last week in Denver — the Biden-Ryan was hotly anticipated.
Biden, Democratic insiders say, was looking to throw a lifeline to the suddenly struggling Obama re-election campaign.
Ryan, on the other hand, was hoping to give Romney's suddenly surging campaign yet another shot in the arm with less than a month until the Nov. 6 vote.
Nonetheless, Biden's strong showing could be a distant memory if Obama is bested once again by Romney during their second showdown next week in Hempstead, NY. The president has vowed that won't happen.
The 90-minute vice-presidential clash pit two men of different generations and wildly varying political philosophies against one another.
Biden, 69, has long been a passionate defender of the American social safety net.
Ryan, 42, is an Ayn Rand aficionado who has proposed deep budget cuts and turning Medicare, one of America's most cherished entitlement programs, into a privatized voucher system.
They were also the first two Catholics to square off in a national political debate — although the strains of Catholicism they each embrace are also starkly different.
Biden is pro-choice and in favour of same-sex marriage; Ryan is avidly pro-life and opposes gay matrimony. The Washington Post dubbed the Kentucky debate as the "Catholic Thrilla in Manila."
Romney surprised pundits in August when he tapped the socially conservative Ryan as his running mate given he was expected to opt for a more moderate No. 2. Ryan's Medicare proposals were expected to cause Romney trouble in the crucial swing state of Florida, home to millions of seniors.
Ryan was also harshly criticized — mostly by liberals, but also by some conservatives — for his speech to the Republican National Convention in Tampa in late August. Some of his allegations against Obama during his remarks were significantly exaggerated.
Biden, meantime, has caused the administration some occasional moments of embarrassment, most notably in May, when he came out in strong support of same-sex marriage. That was at odds with Obama's stance at the time, and was thought to have forced the president to announce his change of heart earlier than planned.