Democratic Illinois Gov. Pat Quinn, ahead of GOP rival Bill Brady on Thursday by 19,400 votes, said his lead is "insurmountable" with 100 percent of all precincts reporting.
Election authorities have not yet declared Quinn the winner. Brady has declined to concede as of Thursday afternoon.
Quinn's election would be the major bright spot for Illinois Democrats, who lost President Obama's Senate seat to Republican Rep. Mark Kirk. In addition, two, and likely three Illinois House Democrats lost their seats.
Quinn became governor in Jan. 2009, when he moved up from the lieutenant governor's office after former Gov. Rod Blagojevich was impeached.
This will be Quinn's first full term.
"I think our lead is insurmountable -- I think it may grow a little bit," Quinn said at Manny's Deli just south of Chicago's Loop on the near South Side, a favorite of the city's politicos, cops and corn beef lovers.
"The numbers are basically there. The basic laws of arithmetic are on our side. Those wondering about the results of the election, they just have to look at the count right now and that will tell them the results right there," the Chicago Sun-Times reported.
Quinn's win is "decisive," campaign manager Ben Nuckels said in an e-mail to supporters.
"While we will wait for every vote to be counted, our current lead is more than 19,000 votes. We don't see a path to victory for Senator Brady, and we believe we have won."