It's all about Anderson Cooper.

At least he's a major reason CNN gave for beating Fox News Channel during prime time in a key demographic.

The Atlanta-based network had a bigger number of viewers age 25-54 for the first quarter of 2008, taking bragging rights in the category away from Fox News for the first time since 2001, Nielsen Media Research said Tuesday.

For that age group, CNN averaged 444,000 viewers during the prime-time slot —- 8 to 11 p.m. —- soaring 87 percent compared with a year earlier.

News Corp.'s Fox News averaged 430,000 viewers, up 10 percent.

Though Fox was still No. 1 in prime time for all ages and other categories, CNN officials said winning the 25-54 demographic is crucial from a business perspective.

"That's the demographic that advertisers are buying," CNN/US President Jonathan Klein said.

He gave a lot of credit to "Anderson Cooper 360," which had an average of 456,000 viewers in that age group. Its Fox News rival, "On the Record with Greta Van Susteren," brought in an average 397,000 viewers age 25-54.

Derek Baine, an analyst at SNL Kagan Research, said the heated Democratic presidential race between Sens. Hillary Clinton and Barack Obama has helped, too. That contest is tying viewers to CNN more so than Sen. John McCain's smoother march to the GOP nomination has captured Fox News viewers.

"The Republican Party is going out of favor, and programming on Fox News Channel has always had a more conservative spin than CNN," Baine said. "McCain is less interesting even to the Republicans."

The tempo for CNN's quarter was set early on. The network beat Fox News the night of Jan. 8 —- the New Hampshire primary —- averaging 3.29 million viewers to Fox's 3.06 million.

Still, Fox News has plenty to crow about among the quarterly numbers.

For prime-time viewers of all ages, Fox News brought in an average 1.8 million viewers to CNN's 1.25 million.

During the entire day for the 25-54 group, Fox News garnered an average 257,000 viewers. CNN had an average of 221,000.

A Fox News spokeswoman declined to comment for this story.

CNN's current prime-time lineup includes "Election Center" at 8 p.m., followed by "Larry King Live" and "Anderson Cooper 360." They go up against Fox's "The O'Reilly Factor," "Hannity & Colmes" and "On the Record with Greta Van Susteren."