HOLLYWOOD — The late-night ratings race continues to evolve, with CBS’ “Late Show With David Letterman” notching its first total-viewer victory over NBC’s “The Tonight Show With Conan O’Brien.” Letterman had not logged a weekly victory over “The Tonight Show” since 2005.

For the week ending last Friday, Letterman drew an average of 3.5 million viewers, compared with 3.3 million for O’Brien, according to data released Thursday by Nielsen Media Research. O’Brien took over June 1 from Jay Leno, who routinely pulled in more than 5 million viewers.
The good news for NBC is that O’Brien has maintained a strong lead over Letterman in the advertiser-friendly demographic of adults aged 18 to 49, and “The Tonight Show” is doing particularly well among adults aged 18 to 34.