Newt Gingrich won the Republican U.S. presidential primary in South Carolina on Saturday, with Mitt Romney behind in second, television networks projected.

Fox News, ABC and NBC projected Gingrich, the former speaker of the House of Representatives, as the winner but CNN had not yet called the election.

Gingrich's victory means that three different candidates have won the first three contests in the state-by-state battle for the Republican presidential nomination to face Democratic President Barack Obama on November 6. Rick Santorum won the Iowa caucuses on January 3 and Romney won the New Hampshire primary on January 10.

Romney's second-place showing came after he slipped in the polls in recent days under criticism over his reluctance to release personal tax information and his admission that he pays a much lower tax rate than many Americans. Romney, the former Massachusetts governor and former chief of private equity firm Bain Capital, is one of the wealthiest men ever to run for president.

The Gingrich victory followed disappointing finishes in the first contests in Iowa and New Hampshire.

The next contest on the calendar is the important Florida primary on January 31. It will be the largest state yet in the nomination battle and one that will require the candidates to spend quite a bit of money on advertising in many cities.

(Reporting by Deborah Charles; Editing by Will Dunham)