Former Dollar General CEO David Perdue won the Republican nomination for U.S. Senate in Georgia on Tuesday, defeating Rep. Jack Kingston in a close race that went down to the wire.

Perdue will now face Democratic nominee Michelle Nunn in what's expected to be a closely watched race both parties are expected to contest. They will compete for the seat of retiring Sen. Saxby Chambliss (R).

Republicans need to gain six seats to win the Senate majority. Democrats, defending many more competitive seats, view Georgia as one of their two best pickup opportunities, along with Kentucky.

With nearly all of the vote tallied, Perdue led Kingston 51 percent to 49 percent.

The outcome is a blow to the U.S. Chamber of Commerce, which made a sizable investment on behalf of Kingston. The nation’s largest business organization had been on a hot streak. It supported Sen. Thad Cochran (R-Miss.) and Rep. Mike Simpson (R-Idaho), who each defeated challengers backed by national tea party groups earlier this year.

Tea party groups stayed on the sidelines in the Kingston-Perdue showdown. Neither candidate pitched himself as a tea party hero.

The Chamber was the biggest spending third-party group, dishing out more than $2.3 million to help Kingston, according to data compiled by the Center for Responsive Politics.

Kingston emphasized his government experience during the campaign, even at a time when polls show Congress is woefully unpopular. He also secured the endorsement of notable current and former lawmakers.

Tuesday’s runoff was conducted because no candidate won a majority in the May 20 Republican primary. Perdue finished first that day with 31 percent of the vote.

Perdue will now turn his attention to Nunn, a philanthropist who used to head up Points of Light, a nonprofit encouraging volunteerism.

Nunn has been one of the most prolific fundraisers of the year. Polls show her running competitively against Perdue.

Perdue, a cousin of former governor Sonny Perdue (R), ran in the primary as an outsider ready to shake up Washington. He used his personal wealth to help finance his campaign.

But his wealth and business dealings will be a target for Democrats. Kingston sought to attack him for both.

In a debate, Kingston knocked Perdue for living “in a gated community" and accused him of being out of touch with everyday voters. Perdue said he would make no apologies for his success.

"It’s clear multi-millionaire David Perdue is only looking out for himself," said Democratic Senatorial Campaign Committee executive director Guy Cecil in a statement responding to Perdue's win.

National Republican Senatorial Committee Chairman Jerry Moran (Kan.) countered in his own statement: "David's experience in the private sector will be put to good use in Washington, and his firsthand experience in creating thousands of good paying jobs will help Georgians."

Three U.S. House districts in Georgia also held runoffs Tuesday, including Kingston’s. There, state Rep. Buddy Carter defeated tea-party backed retired Army Ranger and surgeon Bob Johnson. The district leans Republican.

In the district being vacated by Rep. Phil Gingrey (R), who ran for Senate, tea party-backed state Sen. Barry Loudermilk easily defeated former congressman Bob Barr, the 2008 Libertarian nominee for president.

In the conservative 10th district, Baptist minister Jody Hice defeated businessman Mike Collins. Rep. Paul Broun (R), who also ran for Senate, is vacating the seat.