Updated

Illinois Republicans chose state senator and dairy magnate Jim Oberweis to challenge powerful, three-term Democratic Sen. Dick Durbin in November, as the party fights to remain relevant in a state in which Democrats hold almost all statewide offices and a substantial majority of congressional and legislative seats.

Oberweis, 67, of Sugar Grove, insisted he had greater name recognition than his primary opponent, Downers Grover businessman and political newcomer Doug Truax, because of the chain of ice cream shops his family owns and his previous campaigns for U.S. Senate.  But he also heavily outspent Truax.

The decision also was crucial because the Senate candidate tops the GOP ticket, just above a governor's race that the party believes it can win after more than a decade of Democratic control.

Oberweis, who said he would serve no more than two terms in the Senate if elected, said he hopes to help the GOP retake control of the U.S. Senate to "change the direction of this country."

The 43-year-old Truax, who owns a health insurance consulting firm, had the support of former U.S. House Speaker Newt Gingrich and U.S. Rep. Aaron Schock, a Peoria Republican, but it was not enough.

Nathan Piper, 21, a political science major at the University of Illinois at Springfield, said Oberweis got his vote on name recognition alone. He knew little about Truax.

"I was at Republican Day at the (state) fair and I probably saw him (Truax) there, but otherwise, I didn't know who he was," Piper said.

Veronique Escalante, a 40-year-old consultant from Glen Ellyn, said she voted for Oberweis because he "runs a successful business."

The GOP hopes to at least give Durbin a scare, but after 32 years in Washington, he has no primary opposition and a big war chest. Even so, some political observers consider Durbin vulnerable because he helped get President Barack Obama's troubled health care program signed into law.

Republicans also hope to undo a near-Democratic sweep of contested congressional seats two years ago -- and hold on to those they won. Democrats now control 12 of the state's 18 seats.

First-term U.S. Rep. Rodney Davis, who kept the 13th District in Republican hands by only a slim margin two years ago, beat out two challengers on Tuesday, including Harvard law school graduate and former Miss America Erika Harold. He will face Democrat Ann Callis, the former chief circuit judge in Madison County who won her primary race, in what could be one of the most watched races in the country.

Harold, a conservative who is biracial, had been praised as someone who could help the GOP broaden its support among voters after losses in 2012. But the party has rallied around Davis, believing the incumbent has a better shot at retaining the seat that stretches from Urbana to Decatur to the outskirts of St. Louis' eastern suburbs.

In another closely watched race, four Republicans were vying for a chance to take on U.S. Rep. Bill Foster of Naperville to represent northern Illinois' 11th District. Foster, a former scientist at the Fermi National Accelerator Laboratory, is serving his second one-term stint in Congress.

The GOP also is trying to hold on to the Illinois treasurer's office after incumbent Dan Rutherford gave up the seat to run for the Republican gubernatorial nomination.

Former House Republican leader Tom Cross beat his primary opponent, DuPage County Auditor Bob Grogan, and will face Democratic state Sen. Mike Frerichs of Champaign in the November general election.

"I think what tonight says about our win is that people are ready for change," Cross said. "They're focused on the financial conditions of the state. They want a balanced budget, they want less taxes; we've been strong about that."

Unions teamed up to target three Democratic incumbent House members from Chicago who voted to cut state worker retirement benefits, defeating six-term state Rep. Toni Berrios. State Rep. Jaime Andrade Jr. survived a four-way primary, while Rep. Christian Mitchell was leading in early returns.

House Republican state Rep. Ed Sullivan of Mundelein won despite being targeted by conservative family groups after voting to legalize gay marriage. Rep. Ron Sandack of Downers Grove was also targeted, but still waiting to learn the outcome.