Illinois Republicans delivered a decisive victory to Mitt Romney in the state’s presidential primary Tuesday, crushing Rick Santorum in what amounted to the first big-state head-to-head contest among the front-runners for the GOP nomination.

With 98 percent of the state’s precincts reporting, unofficial results showed the former Massachusetts governor with 47 percent of the vote to Santorum’s 35 percent. The other two candidates in the race, Newt Gingrich and Ron Paul, made only token campaign efforts in Illinois and were trailing badly.

Even more important for Romney, he swamped Santorum by winning 39 of the 54 elected delegates up for grabs in the state. Santorum had only five, though votes were still being counted in several Downstate congressional districts where he ran strongest.

“What a night. Thank you, Illinois. What a night. Wow!,” Romney said to supporters at his victory party at a Schaumburg hotel shortly after 8 p.m. “Tonight we thank the people of Illinois for their vote and for this extraordinary victory.”

Savoring a victory in President Barack Obama’s home state, Romney framed the general election as a “defining decision” for the American people. “This election will be about principle. Our economic freedom will be on the ballot. … It’s time to say this word: enough.”

Santorum, who had already moved on to his home state of Pennsylvania, told a rally in Gettysburg that he had congratulated Romney but still performed well in Illinois.

“If you look at what’s going to happen tonight, we’re going to win Downstate, we’re going to win central Illinois, we’re going to (win) western Illinois,” he said. “We won the areas that conservatives and Republicans populate. We’re very happy about that. We’re happy about the delegates we’re going to get too.”

The results provided the former Massachusetts governor with a sizable victory and also resurrected the aura of inevitability that his campaign has tried to project, only to be thwarted by close elections and even defeats in other states.

Yet low voter turnout throughout Illinois raised questions about Republican enthusiasm for any of the presidential contenders, particularly in a state where the GOP has long chafed at its minority status to Democrats and finally had a chance to influence a national nomination.