Diaz-Balart was locked in an unexpectedly close reelection battle against Democrat Nicole Locklin after the state's new congressional map added heavily Democratic portions of Broward County to his district. The new District 26 stretches across parts of Miami-Dade and Broward counties.

Diaz-Balart held a narrow lead over Locklin. NBC6 political analyst Alex Penelas said the redistricting effort made Diaz-Balart's race considerably more competitive.

"When you see someone like Mario Diaz-Balart, who's been in Congress for over 20 years, hold on to his seat by maybe 1,000 votes, it's specifically the result of this redistricting effort because reliably red areas were taken away from his district so that they could help Republicans in neighboring districts," Penelas said.

The contest drew attention because of the new map's impact on a longtime incumbent. Diaz-Balart, a Republican, has represented South Florida in Congress for more than two decades. The redrawn district forced him to compete in territory that included heavily Democratic areas of Broward County, turning what is typically a safe seat into a closely watched race.

The result underscores how redistricting can reshape political fortunes in South Florida, where demographic and political lines are closely contested. The new district's boundaries, which combine parts of Miami-Dade and Broward, will shape representation for residents across both counties in the coming term.

NBC News projected Diaz-Balart as the winner on Monday. The race had been closely watched as an indicator of how the state's new congressional map affects incumbent Republicans and the balance of power in Washington.