HOLLYWOOD — The battle of the Davids propelled Wednesday's "American Idol" finale to one of the show's best numbers ever, with 31.7 million viewers tuning in.

Rocker David Cook's victory over teen crooner David Archuleta capped a historic season for Fox, which, amid the disruptions of the three-month writers strike, became America's most-watched network for the first time. It also notched its fourth straight season as No. 1 in adult viewers ages 18 to 49, according to data from Nielsen Media Research.

The 2007-08 TV season officially ended Wednesday.

The high viewership for "Idol's" Season 7 finale came as something of a surprise because the show had received lower-than-expected ratings this season. As recently as earlier this month, "Idol" retreated to some of its softest numbers in years.

But the matchup between Cook and Archuleta evidently proved irresistible. In fact, the two-hour episode was the third-most-watched "Idol" finale, after the 2006 showdown between Taylor Hicks and Katharine McPhee (36.4 million) and the 2003 face-off between Ruben Studdard and Clay Aiken (38.1 million).

Last year's contest between Jordin Sparks and Blake Lewis drew 30.7 million.

The "Idol" finale was a welcome dash of good news for the broadcast TV industry, which has been brought low by the writers strike and ongoing viewer defections to cable.

Every network except Fox saw significant ratings declines this season, including CBS, which shed 16 percent of its average total viewers compared with last season.