Rauner, making his first bid for public office, was credited with re-energizing the state GOP with resources and a statewide push for term limits that ultimately was kept off the ballot. The matchup was one of the most competitive nationwide and shattered fundraising records. Rauner put more than $25 million of his own money into the race.
The contest remained close throughout. Quinn appealed to voters to stick with his plan to raise the minimum wage and mend the state budget by extending an income tax increase that's set to drop on Jan. 1. Rauner argued that re-electing Quinn would only perpetuate Illinois' long-running financial problems.
The wealthy venture capitalist and first-time candidate from Winnetka carried central and southern Illinois as well as the collar counties of Chicago. He also held his own in the heavily populated and heavily Democratic Cook County — the place where Quinn needed to dominate to claim victory. With more than 90 percent of precincts reporting, Rauner led Quinn by about 4 percentage points.
Quinn aides said they were awaiting outstanding ballots in Chicago and Cook County, including mail-in and provisional votes.
"The governor feels it's very important for every voice to be heard and every ballot to be counted," Quinn spokeswoman Brooke Anderson said. "Every vote should be counted before determining who is the next governor."
Rauner launched his gubernatorial run with a signature-driven effort calling for term limits and other changes to the Illinois House and Senate, saying he'd help clean up Springfield. Courts later found the measure unconstitutional for the ballot.
Democrats responded with visits from top party leaders and a fierce campaign to boost turnout.
Quinn focused on issues he said affected working people, including raising the minimum wage, and tried to paint Rauner as an out-of-touch multimillionaire. His efforts were bolstered by a coordinated Democratic campaign to boost turnout in the midterm election, which included a record five ballot measures on issues including birth control coverage, a tax for millionaires and voters' rights.
Labor unions also worked against Rauner after he threatened to rein in "government union bosses."
Preliminary results of an exit poll conducted for The Associated Press and television networks showed Quinn was getting support from Chicago, people earning less than $50,000 a year and those who strongly approved of President Barack Obama's performance. Rauner was faring well in Chicago's collar counties and central and southern Illinois, and among white voters and those who believe government is doing too many things that should be left to businesses and individuals.
John Ray, a lifelong Democrat and retired union painter from Springfield, said he was so disenchanted with Illinois' economic course that he made the leap for Rauner, a first-time candidate promising to use his experience as a private equity investor to create jobs and prosperity.
"I just wanted to see what the change would be," said Ray, 73.
The exit poll also showed Quinn was getting support from Chicago, people earning less than $50,000 a year and those who strongly approved of Obama's performance.
Rodney Lane, a 41-year-old mechanic from Chicago, said he appreciated Quinn's attention to issues affecting everyday people.
"I respect him a little more," Lane said.
But the incumbent was dogged by ethical questions over a botched anti-violence program Republicans deemed a "political slush fund" and a federal lawsuit alleging patronage hiring in his Department of Transportation.
Rauner seized on both issues and both sides got nasty at times.
Rauner referred to Quinn numerous times as a "failure." A Rauner campaign staffer in a fake nose dressed as "Quinnocchio" often tailed the governor at public events, accusing him of telling lies.
Meanwhile, Quinn accused Rauner of "profiteering" and getting rich off of others' misfortune. His campaign once held a news conference on a Chicago beach to illustrate questions about Rauner's reported holdings in the Grand Cayman Islands.
Rauner, 58, has said he plans to move to Springfield and live in the Governor's Mansion. Quinn, 65, had said if he won it would be his last term as governor.
Associated Press writers Don Babwin in Chicago, Jim Suhr in Belleville, David Mercer in Urbana and Kerry Lester in Arlington Heights contributed to this report.