Republican presidential candidate Ted CruzTed CruzThe Trail 2016: Fight night Google backs Obama's internet transition plan Steve King asks: Will Clinton be ‘on her meds or off her meds’ for debate? MORE captured a win in the Idaho primary Tuesday night.
NBC News called the race for Cruz just before midnight Eastern time, less than an hour after polls closed in the state. Fox News called it moments later.
Rep. Raúl Labrador (R-Idaho), an influential member of the conservative House Freedom Caucus, had endorsed the Texas senator.
With 52 percent of precincts reporting, Cruz held a 15-point lead over Trump. But the real estate mogul delivered a strong night, posting victories in Mississippi and Michigan.
Trump's win in Mississippi dealt a blow to Cruz in a Southern state with a large population of evangelicals and social conservatives. Cruz had sought to court those voters but failed to clinch a victory.
While he still lags behind Trump in the overall delegate count, his victory in Idaho gives him bragging rights as the only candidate to best the GOP front-runner on Tuesday.
Cruz continues to position himself as the viable anti-Trump alternative and has called on his fellow GOP rivals to coalesce behind a candidate to take him on.
Cruz will likely split the delegates in Idaho, which awards 32 delegates on a proportional basis.
But Rubio, who currently sits 2 points below the 20 percent threshold, might walk away with none.
So far, the Florida senator has failed to win any of Tuesday's contest, but polls were still open in Hawaii early Wednesday morning.
Idaho's victor in 2012 was Mitt Romney, who ultimately won the GOP's nomination.