U.S. Republican presidential candidate Mitt Romney has pulled off a convincing win in Tuesday's Illinois primary, enlarging his lead in the race for the party's nomination.

With nearly 100 percent of all voting precincts counted, Romney has won 47 percent of the vote, well ahead of his main rival, former U.S. Senator Rick Santorum, who won 35 percent.

The other two Republican candidates, Ron Paul and Newt Gingrich, finished far behind.

The win in Illinois gave Romney another boost to his campaign, which has failed to win support from religious conservatives who have strongly supported Santorum during the nominating contest. Romney's well-funded and better organized campaign also gave him an advantage over Santorum.

The win in Illinois gives Romney a majority of the state's 54 available delegates and put him closer towards the 1,144 delegates needed to secure the Republican nomination and take on the Democratic incumbent, President Barack Obama, in the November election.

In a victory speech Tuesday night in Chicago, Mr. Obama's hometown, the former Massachusetts governor called for new leadership in the White House.

“Three years of Barack Obama have brought us fewer jobs and shrinking paychecks that many of us believed we were in danger of losing something even more than the value of our homes and our 401ks, after years of too many apologies and not enough jobs, historic drops in income and historic highs in gas prices. A president who doesn't hesitate to use all the means necessary to force through Obamacare on the American public, but leads from behind in the world. It's time to say these words, this word, enough, we've had enough.”

Speaking at a rally in his home state of Pennsylvania, Santorum congratulated Romney, but vowed to stay in the race.

“I've said throughout the course of this campaign, that while other issues are certainly important — the economy, joblessness, national security concerns, the family, the issue of life, all of these issues are important. But the foundational issue in this race, the one that is the cause of the other maladies that we are feeling, whether its in the economy, whether its in the budget crisis that we're dealing with, it all boils down to one word, and that's what's at stake in this election, and it's right behind me on that banner, and that's the word freedom.”

Heading into the Illinois primary, the former Massachusetts governor had won more than 500 delegates, while Santorum's total was in the 200s. Gingrich and Paul trailed significantly.

The Republican nominating race now moves on the southern state of Louisiana on Saturday, which Santorum is expected to win handily, given the state's large numbers of religious conservatives. The next round of primaries occurs in early April, with contests in Wisconsin, Maryland and Washington, D.C.

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