With a strong finishing kick from "American Idol," Fox captured the distinction of America's most popular television network for the first time since it began operation in 1987.

Fox took that title from CBS. It was the only major broadcast network with more prime-time viewers than the previous season, a distinction helped by its telecast of the Super Bowl. Fox didn't show television's biggest event during the 2006-7 season.

The competition between the two Davids on "American Idol" -- winner David Cook and runnerup David Archuleta -- was seen by 31.7 million people on Wednesday, according to preliminary Nielsen Media Research estimates. Last year's finale, won by Jordin Sparks, drew 30.7 million viewers.

Photo Essay: 'American Idol' finale.

Video: FOXNews.com catches up with new 'Idol' David Cook.

Blog: The Scoop on 'American Idol.'

It was a heartening finish for Fox executives, who admitted to concern when the ratings for TV's most popular show faded in recent weeks.

"It's part of the magic of the show," said Kevin Reilly, Fox entertainment president. "It's like a sporting event in that way, the competition takes on surprise and takes on drama. When it came down to the two Davids, it was a great story that created passion."

Although the finale's audience was the second highest in five years, it was slightly down from last year among 18-to-49-year-old viewers, an indication that the "American Idol" audience is aging.

Fox averaged 11.1 million viewers in prime-time this season through Tuesday, up 7 percent from last year. The numbers will probably inch up when the "American Idol" finale is figured in.

CBS was second with 10.5 million viewers. It had the sharpest drop among the big broadcast networks, at 16 percent. Analysts said CBS was particularly hurt by the television writers strike, when it relied heavily on reruns that didn't do as strongly in the ratings as the network anticipated.

ABC was third with 10 million viewers (down 7 percent) and NBC finished fourth with 8.9 million (down 9 percent). The troubled CW network was down 19 percent, with 2.6 million viewers, and faces the loss of professional wrestling next season, one of its most popular programs.

The historic victory left Reilly only mildly excited. That's because Fox cultivates a young, hip image and concentrates its business on the 18-to-49-year-old demographic (where it was the top network for the fourth year in a row).

"We want as many people watching Fox as possible," Reilly said. "We have to be mindful, we have to keep our brand rooted in what it has been historically. We're not looking to turn into CBS."

CBS traditionally has the oldest audience of the major networks.