Pritzker defeated Chris Kennedy, a member of a famous political family, and Daniel Biss, a self-described "middle-class candidate," to advance to what could be the most expensive governor's race in U.S. history.
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The Pritzker campaign released a statement on behalf of he and running mate State Rep. Julianna Stratton saying, "Tonight, we've taken the next step of beating Bruce Rauner and putting Illinois back on the side of working families."
"I will fight today, and tomorrow, and every day of this election and every day after to get our state back on track. I will never forget that you elected me to fight. Together, we have built a campaign in all 102 counties and we are ready to unite this state to defeat Bruce Rauner and move Illinois forward," the statement continued.
Rauner and Pritzker combined to spend more than $120 million out of their own pockets so far on the contest, putting the race on pace to surpass California in 2010 as the nation's costliest governor's race.
Personal wealth solidified Rauner and Pritzker's front-runner status but also made them frequent targets for opponent attacks. Even Kennedy spent $2 million of his own money on the race.
Biss, a Harvard-educated mathematician who gave up teaching to enter politics, set up a website to track what he says is a $171,000-a-day campaign by Pritzker. The Democratic front-runner has been advertising on television from nearly the moment he announced his candidacy 11 months ago.
WATCH: Daniel Biss addresses supporters after primary
Daniel Biss addresses supporters
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Pritzker's opponents also have attacked his connections with overseas trusts in low-tax countries, though he maintains they're focused on charitable giving and that he has no control over them. In response, Biss has called him a "fraud" while Kennedy labeled him a "liar."
But far more damaging were ads that Rauner ran against Pritzker after wiretap audio surfaced of him talking with former Gov. Rod Blagojevich. The ads included a 30-minute infomercial-style ad with the full FBI recordings.
Earlier in the day each candidate made sure to cast their own ballot. Biss made it a family affair, voting in Evanston while giving his daughter a civics lesson in the booth.
"We feel great. It feel like there's a high turnout, a lot of new voters and a progressive electorate that wants a middle class governor," Biss said.
Kennedy and his wife voted in Kenilworth, and then he planned to campaign through the day.
"I feel very confident going in today. I would say this, I realize as we come to the end of the campaign today that there's very little I can do to change the course of the outcome. My future is in the hands of the voters," he said.
Pritzker, who voted early, was making nearly a dozen stops including an Election Day tradition at Manny's Deli.
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"So many people out voting, voting lines are good, it feels like our voters are getting out to vote, our field operation is going and things look really good, I'm excited. And thanks so much to everybody for being here," he said.
Political consultants said it could come down to Pritzker's $70 million personal investment or Kennedy's name recognition.
"It's always been good, that name in the African American community, so you could make an argument for him to win. You can make an argument for JB with $70 million and only 30-something percent to lose, and you could make a good argument for Daniel Biss to kind of leapfrog everybody," said Thom Serafin, political consultant.
"The frontrunner, so to speak, has spent $70 million and you're in a three-way race, so that is unbelievable. With all the benefits of having all the built-in infrastructure, that's sort of unbelievable," said political consultant Delmarie Cobb.
Early voting and absentee ballots suggested high turnout for Democrats and strong interest in the race.
The Associated Press contributed to this report.