New York ? It promises to be the clash of the network titans this television season: CBS vs. NBC.

Round one goes to CBS.

It was the most popular network during opening week of the new season, narrowly beating its top rival. CBS averaged 13.9 million viewers last week in prime-time, while NBC had 13.4 million.

Media executives used to talk about the Big Three, or even Big Four, networks. Now it’s arguably the Big Two, with the Medium Two (ABC and Fox) and Little Three (the WB, UPN and Pax TV) trailing. ABC and Fox both struggled mightily last year in the ratings, and there’s no immediate sign of a turnaround.

The Big Two have most of television’s popular shows: “CSI: Crime Scene Investigation,” “Everybody Loves Raymond,” “Survivor” and the new “CSI: Miami” on CBS; “Friends,” “ER,” “Frasier” and “The West Wing” on NBC.

Of the top 30 shows in Nielsen Media Research’s ratings for opening week, CBS had 13 and NBC had 12. ABC had five.

CBS and NBC also have two high-profile, hyper-competitive leaders in CBS President Les Moonves and NBC Entertainment President Jeff Zucker, who love nothing more than grabbing every possible edge and tweaking each other.

“Les who?” Zucker said.

One way they’re scraping for an advantage: NBC said Tuesday that “Friends” would run an extra two minutes long all season, delaying the show after it, although Zucker said that wouldn’t mean more ads. It could cut into the ratings of rival shows, however. CBS stretched “CSI” an extra minute last week to cram in extra promotional announcements.

With 30.4 million viewers, “CSI” was the week’s most popular drama, beating NBC’s “ER” by nearly 4 million viewers. The Monday night spinoff, “CSI: Miami,” wasn’t far behind, with 23.1 million people watching.

NBC’s comedy “Friends,” likely in its last season, opened with 34 million viewers, the week’s most popular show. “Frasier” and “Will & Grace” also had strong openings.

Besides “CSI: Miami,” both networks also had some promising freshman shows: “Without a Trace,” “Presidio Med” and “Hack” all finished in the week’s top 30 for CBS, while “Good Morning Miami,” “Hidden Hills,” “American Dreams” and “Boomtown” did the same for NBC.

NBC, which won last year’s opening week and the season, was down 1 percent in viewers compared to the same week in 2001. CBS was up 11 percent, according to Nielsen.

NBC concentrates on the advertiser-desired 18-to-49-year-old age demographic, where it easily beat CBS and others for the week.

There will be no losers in this battle, Moonves said.

“At this point in time it’s more about bragging rights than anything else,” he said. “With these performances by both networks, it’s going to mean a great financial year for both of them. Advertising is going to be very strong.”

Meanwhile, ABC averaged 9.9 million viewers, down 16 percent from the year before. Fox’s 7.1 million was up 4 percent from the year before.

ABC has a handful of bright spots: “My Wife and Kids” is poised for a breakout year, and its fellow comedy, “8 Simple Rules for Dating My Teen-aged Daughter,” is doing alright. Yet two of ABC’s new shows the highly-touted “Push, Nevada” and “That Was Then” had disastrous weeks.

The WB had a lot to brag about, up 48 percent from last year behind successes “Smallville,” “Gilmore Girls” and “Everwood.”

l Nielsen ratings of the most-watched television shows are published Thursdays on the TV page.