This is a big win for John McCain. To be able to go into a Republican only primary and win, is huge and could be a sign of things to come. The big question since South Carolina was whether McCain could win with just registered Republicans voting, and he did.

Sen. John McCain won a breakthrough triumph in the Florida Republican primary Tuesday night, edging past former Massachusetts Gov. Mitt Romney and seizing precious campaign momentum for next week’s string of contests across 21 states.

Former New York Mayor Rudy Giuliani was running third, and headed for the exits. Officials familiar with events said his aides were in discussions with McCain’s advisers on a possible endorsement later in the week.

“It shows one thing. I’m the conservative leader who can unite the party,” McCain said in a brief interview with The Associated Press.

“It’s a very significant boost but I think we’ve got a tough week ahead and a lot of states to come.”

The victory was worth 57 national convention delegates for McCain, a winner-take-all’s haul and the largest single prize to date in the race.

Former Arkansas Gov. Mike Huckabee trailed, but told supporters he would campaign on. Texas Rep. Ron Paul was fifth, and last.

Returns from 64 percent of the state’s precincts showed McCain, the Arizona senator, with 36 percent of the vote and Romney, the former governor of Massachusetts, with 31 percent.

McCain’s victory was his first-ever primary win in a state that allowed only Republicans to vote. His previous victories, in New Hampshire and South Carolina this year, and in two states in 2000 came in elections open to independents. He campaigned with the support of the state’s two top Republican elected officials, Gov. Charlie Crist and Sen. Mel Martinez.