Relentless ads promised a showdown for the ages, and Donald J. Trump even made a personal appeal, pledging to post his own pithy commentary on Twitter in real time.

But in the end, many more Americans chose the popular programs “NCIS” and “The Voice’’ over Megyn Kelly’s soft-toned interview Tuesday night with the likely Republican presidential nominee.

Mr. Trump, it turns out, is a ratings bonanza — to a point.

The debut of “Megyn Kelly Presents” drew an average of 4.8 million viewers, according to early Nielsen figures, a respectable number for a prime-time special but less than the audience for, say, one of this presidential campaign’s punchy debates. The first quarter-hour, when Mr. Trump was featured, drew an average of 5.2 million viewers, Fox said on Wednesday.

News programming rarely outpaces entertainment, and Ms. Kelly’s Fox special, trumpeted as her Barbara Walters moment, did not buck that trend. It faced stiff competition in the 8 p.m. time slot: the finale of “NCIS,” the long-running CBS procedural that is a reliable ratings magnet, drew 17.6 million viewers; “The Voice” on NBC attracted about 8.9 million. “Fresh Off the Boat,” the ABC sitcom, fell short of Ms. Kelly’s special, but not by much, with 4.2 million viewers.