(Adds additional election results)
By Mary Wisniewski
CHICAGO, March 18 (Reuters) - Businessman Bruce Rauner narrowly won the Republican nomination on Tuesday to challenge Illinois Governor Pat Quinn, a Democrat who is seen as deeply vulnerable in this left-leaning state ahead of the November election.
Meanwhile, Quinn coasted to a win in his own primary, beating anti-violence activist Tio Hardiman. Preliminary results by Reuters U.S. Election Service had Quinn leading Hardiman about 72 percent to 28 percent.
Republicans are looking to Illinois as perhaps the party's best shot to take out a Democratic incumbent governor. Despite low popularity ratings and Illinois' continuing fiscal problems, Quinn is expected to emerge as a formidable candidate with strong support from the state's labor unions.
"I've been in a lot of tough fights," Quinn said in his victory speech. "Illinois is making a comeback and we know we have a lot more work to do. That's why we're here today. We have work to do on behalf of everyday people."
Rauner, a wealthy businessman who has already pumped $6 million of his own money into the campaign, topped his three Republican rivals with about 40 percent of the vote, according to preliminary results by Reuters U.S. Election Service.
His closest rival, State Senator Kirk Dillard, followed with about 38 percent of the vote.
In his own victory speech, Rauner called Quinn a failure and promised a Republican victory in November.
"Let's bring back Illinois. What that means is we want to restore the opportunity, the quality of life for every family in our state," said Rauner.
Election officials reported low turnout throughout the day.
Voters in the home state of President Barack Obama have chosen a Democratic governor in every election since 2002.
Meanwhile, in the Republican primary to take on veteran U.S. Senator Dick Durbin in November - the No. 2 Democrat in the Senate - Illinois State Senator Jim Oberweis, the millionaire owner of a dairy business defeated businessman and political newcomer Doug Truax for the Republican nomination.
"The state is in deep trouble. Our country is in deep trouble," Oberweis said in a victory speech.
AN OPPORTUNITY FOR PARTISANS
Democrats and Republicans alike are expecting a tough and expensive contest five years after Quinn took over from Rod Blagojevich, a fellow Democrat who is now in federal prison on corruption charges.
"Illinois will be one of the primary focuses of traditional Republican groups and groups that are interested in conservative economic policy," said Kent Redfield, emeritus professor of political science at the University of Illinois at Springfield. "This is an opportunity to flip a state from Democrat to Republican."
Rauner has used his considerable campaign war chest to buy a blitz of radio and TV ads that have helped him build his name recognition and push him past three more experienced opponents - Dillard, State Senator Bill Brady and State Treasurer Dan Rutherford.
Rauner has steered clear of social issues and focused on Illinois' troubled economy. He has also criticized other lawmakers, including Dillard, for taking union money.
Even before all the returns were in, Quinn was already running a TV ad against Rauner blasting him for saying that he was against raising the minimum wage. Rauner later modified his position.
"Quinn wasn't expected to win last time, but the groundswell of support from labor unions and regular folks who like him sort of surprised people," said Dick Simpson, a political science professor at University of Illinois-Chicago. (Editing by Edith Honan and Lisa Shumaker)