Sept. 29 (Bloomberg) -- David Letterman’s “Late Show” won more young viewers than “The Tonight Show with Conan O’Brien” for the first time last week with guests including Barack Obama and Bill Clinton.

The current and former presidents, along with singer Mary J. Blige, helped Letterman, 62, win the week in total viewers and the 18-49 age group advertisers target on at least three of five nights, according to Nielsen Co. data. It was the first face-off for the late-night hosts in a week when both networks aired their new prime-time shows.

The weekly win for Letterman’s show, produced at the Ed Sullivan Theater in Manhattan, is also the first among younger viewers in almost four years, CBS said, citing preliminary Nielsen data. The “Late Show” became the most-watched late- night show overall and began catching up in 18-49 after O’Brien succeeded Jay Leno as “Tonight Show” host in June.

“Letterman has taken his show to another level and really stepped up,” Andy Donchin, director of media investments at Carat North America, a New York advertising agency, said in an interview. “He has a very real opportunity to take over.”

Letterman also benefited from new 10 p.m. shows on New York-based CBS that included “NCIS: Los Angeles,” which tied for the week’s second most-watched program, and “The Good Wife.”

NBC introduced its fall programs the previous week, winning the Nielsen prime-time ratings for the period and helping O’Brien to his biggest audience since June, the network said. “The Tonight Show” aired a rerun on Friday, Sept. 25, after O’Brien, 46, hit his head during a stunt.

Presidential Visits

Final late-night ratings from New York-based Nielsen will be released Oct. 1. Letterman wasn’t available to comment, according to CBS spokeswoman Kimberly Izzo-Emmet.

“This is a single week, and a highly unusual one at that,” NBC said in an e-mailed statement. “The key for us is to win and dominate in the broad demos over a long period of time.”

CBS Corp., owner of the most-watched television network, rose 13 cents to $12.41 at 4 p.m. in New York Stock Exchange composite trading. The shares have gained 52 percent this year. NBC parent General Electric Co., based in Fairfield, Connecticut, fell 5 cents to $16.71 and has gained 3 percent.

President Obama’s “Late Show” appearance on Sept. 21 attracted more than 7.2 million viewers, the most since Oprah Winfrey was a guest in December 2005, and drew 90 percent more younger viewers than the “Tonight Show,” CBS said.

On Sept. 22, former President Clinton and basketball star LeBron James attracted 5.1 million viewers and topped the “Tonight Show” by 9 percent in the younger demographic, according to the network.

Smaller Audiences

Leno’s 10 p.m. show on NBC is furnishing smaller audiences for late local news and “The Tonight Show,” according to data provided by the networks.

“The Jay Leno Show” ranked behind scripted programs on CBS and Walt Disney Co.’s ABC in both total audience and younger viewers, NBC said in statements last week, citing the preliminary Nielsen figures. News Corp.’s Fox network doesn’t air programs at 10 p.m.

“Late night is affected by the networks’ new prime-time schedule and that hasn’t settled out yet,” Donchin said. “It’s still a little early in the game to call a winner.”

To contact the reporter on this story: Andy Fixmer in Los Angeles at afixmer@bloomberg.net

Last Updated: September 29, 2009 16:15 EDT