Washington: Surprising his rivals and scrambling the Republican race for the Presidency Newt Gingrich, the former Speaker of US House of Representatives scored an upset win over Mitt Romney, former Massachusetts Governor, in the South Carolina Republican primary to select the party's presidential nominee to challenge incumbent Barack Obama in the November elections.

Given that for decades the South Carolina Republican primary winner has ended up bagging the party's presidential nominee, Saturday's results came as a big boost for Gingrich.

At the same time it is a big setback to Romney, who was leading the State till a week before and was looking forward to seal his nomination with a win here.

While counting of votes is still going on and it would take time for official results to be declared, Gingrich has taken an accessible lead over his nearest rival Romney with more than half of votes counted.

Gingrich had polled more than 95,000 votes (40 percent of the votes) against Romney's more than 63,000 (27 percent).

Seeing the writing on the wall, Romney conceded defeat and congratulated Gingrich for his victory in South Carolina.

"Tonight I want to congratulate of course Speaker Gingrich and my fellow Republicans in a hard fought campaign here in South Carolina. We're now three contests into a long primary season. This is a hard fight because there's so much worth fighting for," Romney said conceding his defeat at a post-election rally in South Carolina.

"Now this race is getting to be even more interesting," said Romney who won the New Hampshire primary and narrowly lost the Iowa Caucus to Rick Santorum, the former Pennsylvania Senator.

Saturday, he stands on third with 18 percent of the votes.

Ron Paul, the Texas Congressman, came fourth and last with 13 percent of the votes.

Earlier, Gingrich predicted that his win in South Carolina would secure his nomination for the party.

"If we win on Saturday, with your help, I believe I will become the nominee because I do think South Carolina in effect has an enormous impact," he said.

"You've picked the winner of every primary since 1980. I believe we will go on to win Florida and we will go on to win the nomination," he said.

"Mr Gingrich's come-from-behind win just over a week after his fifth-place finish in New Hampshire scrambles the Republican nomination race. It punctures Mr Romney's air of inevitability and gives Mr Gingrich a significant boost going into Florida, where he must surmount Mr Romney's superior organizational and financial edge. Florida's Republican primary will be on January 31".

Terming it as a "stunning" victory for Gingrich, The Washington Post attributed this to the two impressive performances by the former Speaker during the presidential debates in South Carolina this week.

Gingrich's victory came just 10 days after a fifth-place finish in New Hampshire left the impression that his candidacy was all but dead.

Mr Gingrich rode to victory by winning a plurality among a wide swath of important Republican voting blocs, outperforming the rest of the four-person field among evangelical Christians and Tea Party supporters, men and even women, despite the publicity given to problems in his first two marriages.

The four remaining Republican presidential candidates now move to Florida which goes to primary on January 31.

(Agencies)