Sen. Thom Tillis (R-N.C.) declared an early victory on Tuesday night in a race that has not yet been called by election officials or news organizations.
"What we accomplished tonight was a stunning victory," Tillis told supporters at a campaign watch party.
"And we did it!" he added, drawing cheers.
Tillis referred to polls that showed him losing to Democratic challenger Cal Cunningham but he said he always maintained belief in his supporters and campaign volunteers.
Cunningham's campaign didn't respond to a request for comment.
According to Decision Desk HQ, with an estimated 95 percent of the votes counted as of 1:15 a.m. Eastern Time on Nov. 4, Tillis was ahead by nearly 100,000 votes.
North Carolina will count mail-in ballots received by Nov. 6 but the State Board of Elections estimated before the election that approximately 97 percent of the ballots cast would be counted by the end of Election Night. Unless an overwhelming majority are for Cunningham, Tillis will have won reelection.
The seat held by Tillis was eyed by Democrats as a potential flip as they try to gain control of the upper congressional chamber.
Republicans held the Senate 53-47 prior to the election.
Tillis, 60, a former state speaker, will serve a second term if he wins the race.
Cunningham is married with two children.
Both parties later admitted to an affair.
Cunningham, a lawyer, was recruited to run against Tillis by Senate Majority Leader Chuck Schumer (D-N.Y.).