Rauner, Dillard and Brady spent Monday traveling the state to meet with voters and urge them to go to the polls. Organized labor, meanwhile, was encouraging members to pull Republican primary ballots and cast their vote for Dillard, who has been endorsed by three of the state's largest public-employee unions.
The typically left-leaning unions spent more than $6 million on the GOP primary, both in anti-Rauner and pro-Dillard ads. Rauner has raised more than $14 million, including $6 million of his own money — more than any candidate seeking a gubernatorial nomination in state history.
In stops across the state Monday, Rauner warned supporters about the unions' efforts, saying Democratic Gov. Pat Quinn's "allies" were trying to hijack the election. He also has pushed for term limits for legislators, a move he says will end the cozy relationship between "career politicians" and special interests, such as organized labor.
"We're going to change their world, and they know it," Rauner, of Winnetka, said during a campaign stop at an Italian deli in the southern Illinois community of Herrin.
Republicans haven't held the Illinois governor's office since now-imprisoned former Gov. Rod Blagojevich took office in 2003, and Democrats have almost total control of other statewide offices as well as the Illinois House and Senate.
Quinn, who was Blagojevich's lieutenant governor and assumed the office after his boss was booted amid a corruption scandal, faces lesser-known challenger Tio Hardiman during Tuesday's primary. Quinn, who is expected to easily win the Democratic nomination, is seeking his second full term.
Dillard told supporters Monday that he is tested and prepared to take on Quinn, whom Republicans see as vulnerable because of Illinois' many financial problems, including the highest unemployment rate in the Midwest.
"I'm the only candidate that can send Pat Quinn packing in November," said Dillard, of Hinsdale.
Brady narrowly won the GOP nomination in 2010, but he lost to Quinn in the general election. But the Bloomington lawmaker said he built the support and name recognition during that bid to defeat Quinn this time around.
Rutherford, of Chenoa, has done little campaigning in recent days. He has all but conceded defeat after a former employee filed a federal lawsuit accusing Rutherford of sexually harassing him and making him do campaign work on state time. Rutherford has denied the allegations, saying they were politically motivated.
Voters also will choose between two Republicans vying to take on U.S. Sen. Dick Durbin, the Senate's second-ranking Democrat, in the fall. That primary pits dairy magnate and state Sen. Jim Oberweis, who has lost five of his six bids for public office, against political newcomer and West Point graduate Doug Truax.
Also on the ballot are primary races for the Illinois Legislature and state treasurer.
Polls opened 6 a.m. Tuesday and will remain open until 7 p.m.