Rep. Adam Kinzinger (R-Ill.) defeated Rep. Don Manzullo (R-Ill.) in Tuesday's primary — a big win for the rising GOP star and a relief for House Majority Leader Eric CantorEric Ivan CantorEmbattled Juul seeks allies in Washington GOP faces tough battle to become 'party of health care' 737 crisis tests Boeing's clout in Washington MORE (R-Va.), who had endorsed Kinzinger despite howls from Tea Party groups.

Kinzinger led Manzullo by 56 percent to 44 percent with 85 percent of precincts reporting. The Associated Press called the race.

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It was a bitter fight between the freshman Kinzinger and the 10-term Manzullo, and it turned into a proxy battle between the GOP leadership and the conservative grassroots movement.

There was no Democratic candidate running the heavily-GOP leaning district. Kinzinger, therefore, is expected to win the general election.

Redistricting put Kinzinger in a tough spot. Democrats in charge of drawing the map put his home in a heavily Democratic district, seeking to nip his career in the bud. His decision to challenge Manzullo panned out despite the animosity in the race.

Most observers expected Kinzinger to win the race easily, but Manzullo responded ferociously, keeping the race close by blasting the freshman lawmaker for his "Chicago-style politics" and rallying conservative groups to his side.

But while Manzullo had tried to run to Kinzinger's right, the race turned largely on demographics. Both performed strongly in the parts of the district they'd previously represented, but Kinzinger won over the new part of the district by a solid margin. He was also helped by endorsements from Cantor, and fellow Illinois Republican Reps. John Shimkus and Aaron Schock.

“This race isn’t about who’s more conservative — we’re both conservative; everyone recognizes that,” he told The Hill last week. “The people who have worked with him and worked with me are saying for the future of this party and the future of the country I’m the right choice … Don’s a nice guy, but he’s been there 20 years. It’s time to turn the page and get a new generation of leaders."

The primary turned into a proxy war between the Tea Party and House Republican leadership, with Cantor vocally backing Kinzinger, a deputy whip and rising star in the conference, and a super-PAC run by his former staffers spending $50,000 in radio ads against Manzullo.

Soon after Cantor endorsed, the national Tea Party group FreedomWorks jumped in on Manzullo's behalf.

While Manzullo won't be returning to Congress next year, he'll be around for the next few months — and is unlikely to stay quiet about Cantor's involvement in the race.
 
Manzullo told The Hill on Monday that he was “outraged” at Cantor’s endorsement, and called for him to give up his leadership position.

“He needs to step down as majority leader,” Manzullo said. “Members of our conference don’t trust him, and when you don’t trust someone, you need to replace him.”

House Speaker John BoehnerJohn Andrew BoehnerBoehner reveals portrait done by George W. Bush Meadows to be replaced by Biggs as Freedom Caucus leader Scaramucci compares Trump to Jonestown cult leader: 'It's like a hostage crisis inside the White House' MORE (R-Ohio) also donated to Kinzinger’s campaign shortly before the freshman lawmaker announced he would run against Manzullo. BoehnerJohn Andrew BoehnerBoehner reveals portrait done by George W. Bush Meadows to be replaced by Biggs as Freedom Caucus leader Scaramucci compares Trump to Jonestown cult leader: 'It's like a hostage crisis inside the White House' MORE later cut a $5,000 check to Manzullo — the same amount he gave to Kinzinger — and Manzullo said Boehner apologized to him for the earlier donation, saying it’d been a mix-up.

On Monday, Boehner’s political team went out of its way to stress his neutrality in this and all member-on-member primaries.

“It's unfortunate that we've got two terrific members pitted against each other — we wish them both well,” a Boehner political spokesman said before emphasizing that Boehner is neutral and had given to both candidates.

House Majority Whip Kevin McCarthy (R-Calif.) donated to Kinzinger in November, before he’d officially announced he’d challenge Manzullo. Manzullo said that McCarthy had called him to make clear he had nothing to do with the ads from the pro-Cantor super-PAC and was neutral in the race.

Manzullo claimed Monday that other members in the GOP conference are furious at Cantor for getting involved in the race.

National Republican Congressional Campaign Chairman Pete Sessions (R-Texas), who stayed neutral in the primary, congratulated Kinzinger on the race and praised Manzullo.

"Don Manzullo has been a principled conservative leader in Congress, and House Republicans appreciate his efforts to strengthen U.S. manufacturing and end wasteful spending that has expanded government’s overreach into our everyday lives. I wish Don, his wife Freda, and their children all the best in the days and years ahead," he said in a statement Tuesday night.

—This story was updated at 11:25 p.m.