(CNN) Democrat Conor Lamb announced Wednesday that his Republican opponent, Rick Saccone, has conceded in the close special election last week for Pennsylvania's 18th Congressional District.

"Just got off the phone with my opponent, @RickSaccone4PA, who congratulated me & graciously conceded last Tuesday's election," Lamb tweeted Wednesday. "I congratulate Mr. Saccone for a close, hard-fought race & wish him the best. Ready to be sworn in & get to work for the people of #PA18."

Former Saccone campaign spokesman Patrick McCann said he had spoken to Saccone's team Tuesday. "The tweet is accurate," he said.

National Republican Congressional Committee spokesman Jesse Hunt also confirmed that Saccone had conceded.

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The concession means Democrats have won their biggest House victory since President Donald Trump took office -- gaining a seat in a deep-red district that Trump had won by 20 percentage points in the 2016 election.

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