Romney's very bad week in the so-called Palmetto State culminated with Gingrich — whose campaign for president has been left for dead more than once — winning the hearts and minds of the state's family-values voters despite his sordid marital history.
"It is very humbling and very sobering to have so many people who so deeply want their country to get back on the right track," an emotional Gingrich, surrounded by family members, told his raucous supporters as they chanted "Newt can win!"
There was a Canadian element to his lengthy, often rambling victory speech as he maligned the Obama administration for recently rejecting TransCanada's Keystone XL pipeline, a project he erroneously said would bring much-needed oil to Texas from "central Canada."
Prime Minister Stephen Harper is a "conservative and a pro-American," he said, and now Canada will be forced to sell its oil to China.
"An American president who can create a Chinese-Canadian partnership is truly a danger to this country," he said.
Romney, meantime, vowed to fight on despite his humiliating loss in South Carolina, where voters have long suspected the former Masschusetts governor is a secret moderate.
"I don't shrink from competition," he said in Columbia during his concession speech. "We're going to win this nomination and we're going to beat President Obama in November."
But he acknowledged the race "is getting to be even more interesting."
Indeed. In the aftermath of defeat, Romney's campaign was already putting out warnings that their candidate was going to start hitting Gingrich hard in the days before the Florida primary, particularly on matters of character.
Unofficial results had Gingrich winning 41 per cent of the vote compared to Romney at 27 per cent. Rick Santorum beat libertarian congressman Ron Paul for third, at 17 per cent to 13 per cent.
A week ago, Romney's campaign had an air of inevitability after he was thought to have won the Iowa caucuses, the New Hampshire primary and sat atop the polls in South Carolina.
Instead, it turns out that Santorum actually won Iowa. Rather than going three for three, the Mormon multi-millionaire has been victorious in just a single contest as he struggles to explain why he's hesitant to release his tax returns.
The implications of Gingrich's triumph for the Romney campaign were stark and immediate — instead of sealing the nomination this weekend, he has a long primary battle ahead of him as the former speaker of the House of Representatives heads to Florida on a wave of momentum.
Romney's currently sitting atop the polls in Florida with a commanding lead ahead of the Jan. 31 contest, but he was well in front in South Carolina a week ago too, where he also vastly overspent Gingrich in campaign advertising.
His numbers in the Sunshine State are expected to come down in the wake of Gingrich's victory, while a recent Gallup poll suggests support for Romney was falling nationwide as his rival gains ground from coast to coast.
As Romney stumbled and staggered in South Carolina all week, the fiery Gingrich was at the top of his game as he energized the party's base.
During two televised debates, the first in Myrtle Beach and the next in Charleston, audience members leapt to their feet to give him standing ovations as he snidely dismissed tough questions on everything from his remarks on black people and food stamps and allegations from one of his ex-wives that he pushed her for an "open marriage."
In his victory speech on Saturday, Gingrich said he'd challenge U.S. President Barack Obama to seven three-hour debates should he win the nomination.
He also took venomous aim at "media elites," even though Gingrich is well-known to be among the friendliest of the candidates to the reporters covering his campaign.
South Carolina is considered a crucial primary for the Republican party.
Since 1980, every victorious candidate in the state has gone on to win the party's nomination. And yet in 2012's rollercoaster of a race, one with a seemingly endless supply of unprecedented surprises, that current political reality could go up in smoke.
Gingrich's victory, for example, marks the first time that three different candidates have won the first three Republican contests.
It's a particularly sweet moment in the sun for Gingrich.
He was stung just a week ago, when the country's leading evangelicals snubbed him in favour of Santorum, the staunch social conservative who spent years in Congress as a Pennsylvania senator. They cited concerns about the thrice-married Gingrich's personal baggage.
But their endorsement apparently had no impact on South Carolina's Republican primary voters, more than 60 per cent of whom are evangelicals. Santorum even fell in the polls behind Paul at one point, while Gingrich surged and soared past Romney in several polls in the state.
Even allegations from his second ex-wife, Marianne Gingrich, that he wanted her to agree to an open marriage so he could continue his lengthy extra-marital affair with a congressional aide haven't hurt him. Gingrich later married his mistress, Callista Bisek, who's now the third Mrs. Gingrich.
Both Texas Gov. Rick Perry, who dropped out of the race Thursday, and Tea Party darling Sarah Palin, meantime, endorsed Gingrich. Perry acknowledged Gingrich's tawdry marital history in his endorsement, saying everyone makes mistakes.
Romney acknowledged he was in a tough fight in South Carolina at a morning event in Spartanburg with Gov. Nikki Haley, who assured the crowd that Romney would most certainly be releasing his tax returns soon.
"There is every indication this is going to be a very close race," Romney said.
In an apparent attempt to counter Gingrich's demands that he release his tax returns, Romney renewed his call for his foe to provide more information about the nature of the consulting he once did for despised federal mortgage agency Freddie Mac and Fannie Mae.
There was also a glimpse Saturday of Romney being a regular guy following a week in which the wealthy candidate was criticized for being out of touch with most Americans. His son, Tagg, tweeted a photo of Romney doing his laundry.
"Nothing like the glamorous life on the road," Tagg Romney quipped.
Santorum's campaign, meantime, says their man has no intention of dropping out, even more so now that Gingrich has won South Carolina.
Their reasoning? If Romney loses Florida and drops out of the race, the Republican establishment will rally behind Santorum rather than see Gingrich win the nomination since the party's power brokers fear his volatility, question his character and doubt his ability to beat President Barack Obama in November.
"Short of winning, I couldn't be happier with the way things turned out tonight," Santorum told CNN shortly after Gingrich was declared the winner.