Freshman Rep. Adam Kinzinger defeated longtime Rep. Don Manzullo in the first Member-vs.-Member GOP primary of 2012. Kinzinger led 56 percent to 44 percent when the Associated Press called the race just after 11 p.m. EST.

Kinzinger’s victory may partially vindicate House Majority Leader Eric Cantor, whose endorsement of Kinzinger elicited outcries from the House Republican Conference. Last week, a super PAC run by a former Cantor aide also spent $52,000 on a radio ad to boost the freshman lawmaker.

Although more of Manzullo’s current territory lies in the redrawn 16th district, Republicans initially thought Kinzinger had an edge. But in the final weeks of their contest, Republicans saw Kinzinger’s campaign falter, and they gave the advantage to Manzullo heading into the primary.

Kinzinger’s victory is likely to stun many GOP operatives and Capitol Hill aides who dismissed the Air Force Reserve pilot and Cantor’s involvement in his race.

Democrats redrew the Congressional map in Illinois last year, including changing the borders of the 16th district. When they released the map, Kinzinger lived in the heavily Democratic 2nd district, but he opted to run in the 16th instead — a talking point Manzullo frequently used on the campaign trail.

The 16th district is a strong Republican district, and Kinzinger is expected to easily win a second term there in November.