Updated 6:40 a.m. | State Sen. Glenn Grothman has won the GOP  primary by a slim margin in the only open House district in Wisconsin.  

With 99 percent of precincts reporting, the Associated Press called the 6th district primary race for Grothman, who garnered 36.2 percent of the vote in the four-way contest to succeed retiring GOP Rep. Tom Petri.  

State Sen. Joe Leibham trails Grothman with 35.8 percent — or by 215 votes.  

The race was neck-and-neck  in the final days of the primary. Grothman and the other top two contenders, Leibham and state Rep. Duey Stroebel, battled to convince voters  they were the most conservative candidate in the race.  

Grothman gained momentum in the final weeks of the race, which helped push him across the finish line.  

The outspoken firebrand had the support of the Republican district’s most conservative voters, who were among the primary’s most likely voters to turn out. Throughout the campaign, he garnered support from conservatives including popular talk radio hosts and former Sen. Rick Santorum, R-Pa.  

Grothman jumped into the GOP primary before Petri retired, arguing the longtime congressman was not sufficiently conservative. After Petri retired and the primary became more competitive, Grothman proved to be a sufficient fundraiser and helped boost his campaign by loaning it $100,000.  

The state senator will face Democrat Mark Harris, the Winnebago County Executive, in November, and Grothman is expected to win the seat. The Rothenberg Political Report/Roll Call rates the race as a Safe Republican contest.  

South of the 6th district, Democrats in the 1st nominated Rob Zerban to face Republican Paul D. Ryan in the fall. Zerban won 78.8 percent of the vote when the Associated Press called the race with 59 percent of precincts reporting. Zerban bested filmmaker and community activist Amardeep Kaleka, whose father was killed in the Oak Creek Sihk temple shooting in 2012. Zerban, a businessman and former Kenosha County supervisor, challenged Ryan in 2012. That year Ryan won the district with 55% of the vote, the lowest margin of his congressional career.  

But Zerban faces and uphill climb against to beat Ryan in the fall, who has represented the district for 15 years. The Rothenberg Political Report/Roll Call rates the race as Safe Republican .  

Related Stories:

Wisconsin GOP Primary Is Wide Open


Rating Change: Wisconsin Governor


Paul Ryan Unveils Anti-Poverty Program


The 10 Most Vulnerable House Members


Roll Call Election Map: Race Ratings for Every Seat


Get breaking news alerts and more from Roll Call in your inbox or on your iPhone.