The incumbent president's often meandering answers to questions, rife with halting pauses, were in stark contrast to the lively Romney, who often talked over debate moderator Jim Lehrer to energetically tout his domestic policy proposals while criticizing Obama's.
"Gasoline prices have doubled under the president," Romney said.
"Electric rates are up. Food prices are up. Health-care costs have gone up by $2,500 a family. Middle-income families are being crushed. Look at the evidence of the last four years. It's absolutely extraordinary."
As Obama frowned, Romney continued: "Going forward with the status quo is not going to cut it for the American people who are struggling today."
The president, indeed, seemed grim and tentative throughout much of the debate, often staring down at his notes with a pained smile as Romney forcefully defended himself against uneven attacks from Obama on everything from his job creation plans to his tax and education policies.
"Gov. Romney has a perspective that if we cut taxes ... and roll back regulations, we'll be better off; I have a different view," said Obama, adding Romney's tax policies "skew toward the wealthy."
No matter how often Obama suggested otherwise, Romney countered, "I will not reduce the taxes paid by high-income Americans ... I am not in favour of a $5 trillion tax cut."
Obama brushed him off, saying such assurances are mathematically impossible since cash-strapped governments cannot cut taxes across the board, increase defence spending and bring down the national debt — all of which Romney is promising to do.
"The fact is, if you are lowering the rates the way you describe, Governor, it's not possible ... it's math; it's arithmetic," he said.
Yet the president failed to attack Romney even once on the most damaging episode of his presidential campaign — his recently revealed remarks that almost half of Americans won't vote for him because they're government freeloaders.
Nor did Obama mention Romney's controversial years at the helm of Bain Capital, a venture capital firm some have branded a predatory job-killer.
Instead, the usually composed president was on the defensive throughout most of the showdown at the University of Denver, at times looking uncharacteristically panic-stricken.
"When I walked into the Oval Office, I had more than a trillion-dollar deficit greeting me," he said. "And we know where it came from: two wars that were paid for on a credit card; two tax cuts that were not paid for; and a whole bunch of programs that were not paid for; and then a massive economic crisis."
Despite that, Obama said, "we had to take some initial emergency measures to make sure we didn't slip into a Great Depression."
While the Romney campaign celebrated their man's performance — some conservative commentators called it the best showing for a Republican candidate in decades — the spin from Team Obama was immediate.
"The president spoke to the American people like they're adults," Jen Psaki, his travelling press secretary, told ABC News minutes after the debate wrapped up.
After months of often bitterly maligning one another's policies and job performances from a distance, the two men met face to face for only the fourth time in their lives on Wednesday. They shook hands to greet one another just before the debate got under way, chatting briefly and laughing as though they were old pals.
Both seemed nervous as they answered the first question posed by Lehrer, who asked them to delve into their differences on economic policy.
Romney said his plans involved energy independence, promoting more international trade, ensuring Americans have the skills they need to succeed, balancing the budget and championing small business.
Fifteen minutes into the debate, the Republican found his wings, becoming more forceful against Obama, frequently interrupting his answers and ignoring Lehrer's fruitless attempts to wrest back control of the faceoff.
Lehrer, a respected PBS anchorman, was soon trending worldwide on Twitter, the social media platform. A Twitter account even popped up with the handle Silent Jim Lehrer. One of the Tweets: "Um ... I ...."
The president, meantime, never seemed to find his footing and missed several opportunities to exploit some of Romney's considerable vulnerabilities. The debate, indeed, was remarkable for its civility — neither man was unduly nasty towards the other.
Following the showdown, Romney and his family lingered on stage triumphantly. Obama and first lady Michelle Obama made a hasty exit after greeting some of the Romney clan.
While debates haven't historically altered the course of a presidential campaign, millions of Americans tune in for them — as many as 60 million were expected to have watched on Wednesday, the first of three presidential sparring matches. They can often change public perceptions of a politician.
There have been nine sets of presidential debates since the first televised event in 1960 between Richard Nixon and John F. Kennedy.
Nixon, recovering from knee surgery, perspired so profusely that it was thought to have cost him the election as, post-debate, Kennedy squeaked past him in the polls. In 2000, George W. Bush overtook Al Gore following their debates after Bill Clinton's vice president appeared condescending and petulant during their exchanges.
But those were the only two instances in which the politician trailing in the race came from behind, post-debate, to win the election. Romney is hoping to become the third, and several conservative pundits predicted Wednesday's debates will put serious wind in his sails.
The debate "changed the trajectory of the race," said New Jersey Gov. Chris Christie amid what seemed a full-fledged Republican ticker tape parade on various media platforms.
Romney has narrowed Obama's lead in national polls in recent days, although he's still trailing the president in several critical swing states that will decide the outcome of the election.
The debates are considered his last high-profile chance to turn his struggling campaign around —and to fight back against perceptions, skillfully advanced by the Obama campaign, that he's an unfeeling rich man only looking out for his own.
The president's challenge on Wednesday night was to further portray Romney as a remote millionaire, and to deliver short, pithy answers instead of rambling. By most accounts, he failed.
The debate started on a sweet note.
Before their husbands took the stage, Michelle Obama and Ann Romney shook hands and embraced before taking to their positions at the debate venue. Obama opened his remarks by acknowledging his 20th wedding anniversary.
"Twenty years ago, I became the luckiest man alive when Michelle Obama agreed to marry me," he said.
Romney congratulated the Obamas on their anniversary.
"I'm sure this is the most romantic place you can imagine ... being here with me," he joked.
The candidates stage their next debate on Oct. 16 in Hempstead, N.Y. A final showdown will be held Oct. 22 in Florida, while Vice President Joe Biden and Romney's running mate, Paul Ryan, square off next week in Kentucky.