The former House speaker beats former Republican front-runner Mitt Romney in the South Carolina primary.

Updated from 7:31 p.m. EST with Gingrich claiming victory in South Carolina primary.

COLUMBIA, S.C. (TheStreet) -- Newt Gingrich won the South Carolina primary Saturday in what was a sharp blow to former front-runner Mitt Romney.

"Thank you, South Carolina!" Gingrich tweeted. "Help me deliver the knockout punch in Florida. Join our Moneybomb and donate now."

Newt Gingrich

The South Carolina primary is closely watched because its victor has gone on to win every Republican presidential nomination since 1980.

Former Massachusetts Gov. Romney vowed to fight hard. The next contest will be the Florida primary on Jan. 31.

Former Sen. Rick Santorum and Texas Rep. Ron Paul trailed far behind Gingrich and Romney in the South Carolina voting, the AP reported.

Gingrich had risen in the polls throughout the week, and a poll released Saturday had put him ahead of Romney, 40% to 26%.

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Exit polls showed Gingrich with a wide lead among South Carolina conservatives, tea party supporters and born-again Christians, the AP said.

Meanwhile, Romney had a small advantage among moderate and liberal voters, the news agency added.