Handel also pointed to the district's pedigree throughout the campaign, urging Republicans not to let Democrats "steal" a seat that became a proxy for the national dynamics in Washington.
With 81 percent of precincts reporting, Handel had won the district with 52.5 percent of the vote compared to the 47.5 percent won by Ossoff.
"The people of the Sixth District are going to be looking for someone who's been part of this community for almost 25 years", she told reporters after casting her ballot on Tuesday morning, as several dozen nearby Ossoff supporters chanted "Flip the Sixth".
The suspected gunman was a Democratic supporter and a Republican advert that sought to politicise the attack was condemned by Ms Handel.
Republican Karen Handel on election day after she is projected the victor for the Georgia 6th District special election on June 20, 2017. In special congressional elections in Kansas and Montana they've strained to see green shoots.
But with Democrats falling short in those races, and Republicans expected to hold a SC congressional seat also up for grabs Tuesday, all eyes have turned to Georgia.
Republican Karen Handel won a nationally watched congressional election in Georgia, dealing a massive defeat to Democrats in what's being recognized as the most expensive House race in U.S history, with a price tag that may exceed $50 million.
Democrat Jon Ossoff on June 20, 2017, lost to Republican Karen Handel in Georgia's 6th Congressional District race. Commenting on a SurveyUSA poll in late May showing the Republican trailing Ossoff by a margin of 51-to-42 percent districtwide, veteran Georgia GOP consultant Matt Towery complained that "Karen's big mistake was to avoid Trump in her campaign ads".
It also calls into question whether Democrats can sustain the energy fueling the party's anti-Trump resistance after losses in four consecutive special elections - including Kansas, Montana and SC.
In the special elections for House seats vacated by Republicans who wound up in President Donald Trump's Cabinet, Democrats went 0-for-4.
DeKalb County officials said the problem was resolved by 7:30 a.m. but they want voters to have a full 12 hours to cast ballots in the runoff between Republican Karen Handel and Democrat Jon Ossoff. Her win protected GOP's majority in the 24-seat House and their hold on the 6th Congressional District in Atlanta's northern suburbs, retaining a seat that has been with the Republicans since 1979, Politico reported. She becomes Georgia's first female Republican member of the U.S. House.More news: Pentagon: 3 U.S. soldiers killed, 1 wounded in Afghanistan
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The former Georgia secretary of state won by nearly 4 points, beating Jon Ossoff, a 30-year-old documentary filmmaker and former congressional staffer - 51.9 percent to 48.1 percent.
"It's that fighting spirit, that perseverance and tenacity that I will take to Washington", she said on Tuesday night.
The seat has been vacant since Trump tapped Republican Tom Price to serve as his health secretary.
But while Republicans were facing a sobering reminder of their president's poor approval ratings, Handel steadied the ship in a district that only narrowly backed Trump in last November's vote.
Handel, her own campaign flooded with outside donations, has kept the race tight, emphasizing her area roots. He resides in Atlanta, a few miles south of the 6th District's southern border.
In victory, she commended Ossoff and pledged to work for his supporters.
"My pledge is to be part of the solution, to focus on governing", she said.
"This was not the outcome any of us were hoping for, but this is the beginning of something much bigger than us, so thank you", Ossoff said.
Contrary to the chants at Handel's victory party, she insisted for months that voters' choice had little to do with Trump.
Handel, 55, embraces her experience as a statewide and local elected official. She also welcomed a parade of national GOP figures to Atlanta to help her raise money, with Ryan and Vice President Mike Pence and House Speaker Paul Ryan holding fundraisers following Trump's April visit. He raised $23 million for his campaign, but most of that came from outside of Georgia from liberal enclaves like NY and California.
"Gone are the days of Blue Dogs who actively campaign as Republicans", said Adam Green, the co-founder of the Progressive Change Campaign Committee. "I think in the 6th District we have a chance to make a decision about who's going to lead us whether the president is there or not there, whether his policies are good or bad".