Story highlights With 83% of the vote in, Romney has 83% of the primary vote in Puerto Rico

Romney and Santorum are locked in a tight race in Illinois

Romney now has 518 delegates, more than twice anyone else, CNN estimates

Romney campaigned in Illinois, while Santorum is in Louisiana

Mitt Romney heads in to Illinois's presidential primary this week with a handy win in Puerto Rico, pocketing the territory's 20 GOP delegates in a bruising race that has become a numbers game for the Republican nomination.

With about 83% of total ballots accounted for early Monday in Puerto Rico, Romney had garnered more than 98,000 votes -- or 83% of the total -- based on unofficial results obtained from local party and election officials.

Rick Santorum was a distant second, at 8% with slightly more than 9,500 votes.

The other two candidates, former House Speaker Newt Gingrich and Texas Rep. Ron Paul, were barely registered in the race with 2,431 votes, or 2% of the vote, and 1,452 votes, or 1%, respectively.

Even as the vote was being counted in Puerto Rico, Romney, Santorum and the other candidates were already on the mainland vying for delegates in Illinois and Louisiana.

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Illinois holds its primary on Tuesday and Louisiana on Saturday.

CNN's latest delegate estimates show Romney with 518 delegates to Santorum's 239. Gingrich has 139 delegates, and Paul, the libertarian champion, has 69 delegates. To secure the nomination, 1,144 delegates are needed.

Santorum, the former Pennsylvania senator, was in Louisiana late Sunday, where he is expected to win the primary.

Romney was in Illinois where polls indicate he holds a small lead over Santorum, with Gingrich and Paul well behind.

Romney framed his win in Puerto Rico as the territory's desire for a candidate that "most represents their feelings" -- and especially their desire to nominate some who can bring about a stronger economy and a smaller government.

He also said his party can appeal to Latinos, and win the presidency, with a low-tax, pro-business message.

"Those people who don't think that Latinos will vote for a Republican need to take a look in Puerto Rico," said the former Massachusetts governor, noting that the territory's governor and its legislative leaders are conservative.

"Hispanic voters are going to vote for Republicans if we stand for something -- conservative principles that bring growth and good jobs and rising home values. That's how we're going to win, and we're going to get Latino voters to help us out."

Romney had entered the contest in Puerto Rico as the favorite. He was largely backed by the island government's political establishment, including Gov. Luis Fortuno, who campaigned with Romney last week.

Santorum, the former Pennsylvania senator, created a small political firestorm on the island in the days leading up to the primary when he said English should be the principal language in Puerto Rico before it could gain statehood. Puerto Rico will vote on a statehood referendum in November.

After arriving in Puerto Rico on Friday, Romney said he would have "no preconditions" on language for Puerto Rico to gain statehood, though during a CNN debate in January he said English should be the nation's official language.

Santorum immediately hit back, accusing Romney of flip-flopping.

Romney fired back that English has been the official language of the government in Puerto Rico for more than 100 years.

The heated, see-saw allegations between the two candidates have marked much of the race for the GOP nomination, which Sen. John McCain, R-Arizona, called "the nastiest I've ever seen" during an appearance Sunday on NBC's "Meet The Press."

Puerto Rico's primary came two days before the showdown in Illinois, where 54 delegates will be awarded proportionally and polls show a tight race between Romney and Santorum.

Asked over the weekend while campaigning in Missouri about whether a win in Illinois would mean he'd win the nomination, Santorum said: "We feel very, very good about it. Let's put it that way. Really good about it."

Santorum also challenged Romney's assertion that his business experience is one of his strongest credentials, telling CNN's Candy Crowley on "State of the Union" on Sunday that, "If Gov. Romney thinks that he is the CEO of America and can run and manage the economy, he doesn't understand what conservatives believe in."

Romney's campaign released an ad in Illinois on Friday, attacking Santorum for having "never run a business or a state."

Santorum on Sunday said he had experience in the private sector as a lawyer, but argued that executive experience at a company is not necessary to be commander-in-chief.

"Running a business is not the same as being president of the United States," he said.

Santorum also gave no indication that he has plans to drop out of the race should his campaign reach a point where the delegate math doesn't add up in his favor.

"What I'm hearing is that we want a conservative nominee, that the establishment is trying to push a moderate like they did in 1976 against Ronald Reagan, like they did in 1996 with Bob Dole and what they did with John McCain," Santorum said. "I think conservatives would like an opportunity to nominate a conservative, and that's an opportunity."

Both Santorum and Romney also focused their rhetoric at President Barack Obama, particularly with regard to rising gas prices.

Romney said Obama needed to fire Secretary of Energy Steven Chu and Interior Secretary Ken Salazar for their role in driving up gas prices.

"Given the fact that (Obama has) changed his policies, wants lower gas prices, he needs to fire them and return to the energy policies we need," Romney said during a town hall meeting in Collinsville, Illinois.

Santorum told a crowd in Effingham, Illinois, to remember Obama at the gas pumps.

"When you see that zero come up, when it gets to the $100 range, when you see the zero, think of 'O' for Obama because that's why you are paying that extra amount of money," Santorum said.