By Kevin McDermott and Kathleen Foody

SPRINGFIELD, Ill. — Democratic Illinois Gov. Pat Quinn on Thursday finally won clear title to his party’s nomination for a full term — only to find himself facing a new problem in a running mate with a domestic abuse allegation in his past.

Scott Lee Cohen, 44, a Chicago pawnbroker and political unknown who won the Democratic nomination for lieutenant governor in Tuesday’s statewide primary, was accused in 2005 of domestic battery against a girlfriend, but the woman didn’t follow up on the charges.

Cohen also was accused in a divorce proceeding of steroid abuse and threats against an ex-wife, according to a Chicago Sun-Times account of the divorce record Thursday.

Meanwhile, the Republican gubernatorial contest appeared headed for recount, with just 406 votes separating the two top contenders in final election day ballots.

Quinn on Thursday officially became the Democrats’ nominee for governor in the Nov. 2 election — after an emotional concession by opponent Dan Hynes, who had been considering his own recount challenge because of the closeness of the vote.

Shortly after Hynes’ concession, Quinn suggested Cohen should withdraw from the ticket. Cohen has defiantly refused, saying in several public e-mail messages that his past was revealed before the election to anyone who thought it was an issue.

“I tried to tell everyone about this early on. I wanted to talk about all of these issues, but everyone wrote me off, and said I didn’t have a chance to win,” Cohen wrote in an e-mail. “Now that I’m the Democratic nominee for lieutenant governor, the day after the election, there are questions. I am happy to answer any and all questions; I just need time to do so.”

The abuse allegation was reported in general terms early in the campaign, but it got little media attention in a down-ballot primary crowded with six candidates, most of them better known than Cohen.

Among new details that have come out since the election is that a police account from the incident alleges Cohen held a knife against his then-girlfriend’s throat and hit her head against a wall.

“I was in a tumultuous relationship with the woman I was dating. We had a fight, but I never touched her,” Cohen said in a statement. He has also denied knowing that the woman had been arrested for prostitution.

Cohen said he is trying to get his ex-wife and the ex-girlfriend to come forward and explain the situation. A campaign spokeswoman said Cohen is not in contact with the ex-girlfriend but is trying to reach her.

A Chicago news conference Thursday that Quinn called to accept Hynes’ concession turned almost entirely to the subject of Quinn’s running mate, who was effectively forced on him by Illinois’ unusual system for choosing lieutenant governor candidates.

Cohen “has a lot of explaining to do,” said Quinn. He demanded that Cohen publicly address what he called “a grave issue” and to withdraw as a candidate if he can’t explain it to satisfaction of the party and the public.

“If there are matters that are raised about your conduct that disqualify you from running in a proper way for an election in the fall, then the only appropriate thing is to step aside. And I think that’s what we’re looking at here,” Quinn said.

If Cohen does step aside, the party’s central committee would select a replacement candidate. Quinn said he discussed the process briefly with the House Democratic party leader, Speaker Mike Madigan, on Thursday morning.

Illinois law requires candidates for governor and lieutenant governor to win their nominations separately in the party primaries, then run as a team in the general election. That system has caused problems before, forcing candidates for governor onto tickets with running mates they didn’t pick and sometimes don’t even know.

The biggest shakeup caused by that system was in 1986, when two members of the extremist LaRouche movement won the Democratic nominations for secretary of state and lieutenant governor. The party’s gubernatorial nominee, Adlai Stevenson III, ran a third-party campaign rather than share the ballot with those candidates. Republican James Thompson won the general election with the widest winning margin in Illinois history.

Quinn was installed as governor a year ago, after the removal of indicted ex-Gov. Rod Blagojevich, and is seeking a full term in November.

Hynes — who lost the 2004 Democratic nomination to the U.S. Senate to Barack Obama — challenged Quinn’s nomination, arguing he’d been ineffective in addressing a massive state budget deficit and getting meaningful reform measures enacted.

Quinn started the contest with a double-digit lead over Hynes, but he watched it evaporate in the final weeks before the election, as Hynes’ campaign hammered at Quinn’s income tax hike plan and his controversial inmate early-release program. By election day, polls showed the race too close to call.

Near midnight on Tuesday, with initial returns showing Quinn about 4,000 votes ahead out of some 900,000 cast, Hynes refused to concede. The final count on Thursday extended Quinn’s lead to about 8,000 votes. That was still well within the 5 percent margin that would allow Hynes to seek a recount, but one far less likely to succeed.

In an emotional news conference Thursday morning at his Chicago campaign headquarters, Hynes conceded in a statement that began with a long, deep breath.

“The people have spoken, and the votes have been counted,” he said. “We rose up and fell just a little short.”

The GOP race for governor remained in dispute Thursday and appeared headed for a recount. Final tallies from the GOP primary showed state Sen. Bill Brady edging state Sen. Kirk Dillard by just 406 votes, making a recount challenge all but inevitable.

In other developments from Tuesday’s primaries, Raja Krishnamoorthi conceded defeat in the Democratic contest for comptroller to state Rep. David Miller. And in yet another disputed race, for the Republican nomination for lieutenant governor, state Sen. Matt Murphy on Thursday conceded in his narrow loss to 27-year-old Madison County businessman Jason Plummer, who is vice president of the R.P. Lumber chain.