Tillis staked a claim to a victory in a speech to supporters in Mooresville, but the race had not yet been called.
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With 99.89% of precincts reporting, Tillis led Democratic challenger Cal Cunningham with 48.72% of the vote to 46.95%.
WATCH: Tillis speaks to supporters
Tillis claims 'stunning victory' in hard-fought Senate race
"We were holding up a little bit to hear from my opponent, but we decided we wanted to come over here and talk to you all, because what we accomplished tonight was a stunning victory," Tillis told the crowd.
Tillis has been a staunch ally of President Donald Trump but was criticized by opponents for voting to repeal the 2010 health care overhaul.
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Cal Cunningham has stressed his service in the Iraq War and as a U.S. Army reserve officer and military prosecutor. But in the final weeks of the campaign, he admitted that he had sent sexually suggestive texts to a married woman who was not his wife.
ELECTION 2020 RESULTS: Electoral college votes
With more than 79% of precincts reporting, Tillis had surged ahead by a narrow 48% to 47.73% option.
Election Day comes after the state has seen record early voting by mail and in person.
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Nearly 62% of the state's more than 7.3 million registered voters had cast their ballots by Monday.
FULL NORTH CAROLINA ELECTION RESULTS
The Associated Press contributed to this report.