CHICAGO — Mitt Romney’s image as a stronger challenger for the White House carried him to a major Illinois victory over Republican rival Rick Santorum as many voters stayed home Tuesday despite the rarity of the state actually playing a key role in a presidential primary.

In most years, presidential nominations are settled long before the Illinois primary, but Santorum’s recent string of victories elsewhere made the home state of President Barack Obama relevant in the GOP contest.

Romney, in his victory speech, portrayed himself as an economic expert after years spent in the business world – in sharp contrast to the work Obama did before reaching the White House.

“You can’t learn that teaching constitutional law at the University of Chicago. You can’t even learn that as a community organizer,” Romney said.

Outside the presidential spotlight, U.S. Rep. Jesse Jackson Jr. survived his first serious challenge in years. And in a bitter Republican battle for a seat in Congress, freshman Republican Adam Kinzinger defeated veteran Donald Manzullo.

Turnout was low across the state. In Sangamon County, a Republican stronghold in central Illinois, about 1 in 5 registered voters cast ballots. The numbers were about the same in the GOP-leaning suburbs of Cook County. Kane County saw similar results, although officials said turnout among Republicans topped 50 percent.

The lack of statewide races beyond the presidential contest likely played a role in holding down turnout, particularly among Democrats. It was the first Illinois primary since 2000 that didn’t include a race for U.S. Senate or governor.

Pat Brady, chairman of the Illinois Republican Party, also noted the state enjoyed an extraordinarily warm and sunny first day of spring. The weather may have diverted some people from the voting booth, he said.

Still, Romney won handily, which may repair his dented image as the inevitable nominee.

“I think his campaign has reached a turning point,” said Brady, a Romney supporter. “He’s going to be our nominee.”

All but the most conservative Republicans backed Romney over Santorum, exit polling found.

The former Massachusetts governor was helped by the perception that he is more likely to defeat Obama this fall. Six in 10 voters said Romney had the best chance against Obama in November; only about 1 in 5 said so of Santorum.

Catherine Lopez, a homemaker from the Chicago suburb of Winnetka, was among those concluding Romney would be the best Republican to challenge Obama. “OK, maybe he’s not charismatic,” Lopez said of Romney. “But we’ve had enough charisma with Obama. We need competence.”

With 87 percent of precincts reporting, Romney had 361,116 votes, or 46.6 percent, and Santorum had 272,662 votes, or 35.2 percent. Ron Paul had 9.2 percent, and Newt Gingrich had 8 percent.

Romney won at least 38 delegates in Illinois, with 16 still to be determined. Races for Congress and the Legislature could shape Illinois politics for years to come. Candidates are running in newly drawn political districts, so the officials ultimately elected will have a huge advantage in keeping those seats for the rest of the decade.

The Democratic majority at the state Capitol drew the new maps to make life difficult for Republicans. As a result, Manzullo and Kinzinger were forced to battle for survival in northwestern Illinois, with Manzullo losing after 10 terms in Congress.

On the Democratic side, Jackson was weakened by his admission of an affair and ties to imprisoned former Gov. Rod Blagojevich. But the Chicago political veteran easily defeated former U.S. Rep. Debbie Halvorsen of Crete.

Tony Horton of Chicago said he voted against Jackson because of the affair. “How can I trust you to do the right thing for the state when you ain’t doing the right thing for your household?” Horton said.

In the Legislature, at least four incumbent Republicans would be out after the primary. That’s because eight lawmakers wound up facing each other under the new districts drawn by Democrats.