Conan O'Brien scored a victory over NBC in his debut.
His new TBS show attracted 4.2 million viewers, beating the 3.5 million who tuned into Jay Leno's Tonight Show on NBC and the 3.4 million who watched David Lettermen's Late Show on CBS. Jon Stewart's The Daily Show on Comedy Central drew 1.3 million viewers.
"Conan delivered an extraordinary audience and stands out as the youngest late-night talk show on television," said Steve Koonin, president of Turner Entertainment Networks.
Conan on TBS: For the first show, he's still not over it
In the 18-to-34 demographic, 2.5 million viewers tuned in, making the show's median age 30.
Conan's premiere featured guests Seth Rogen and Lea Michele and a musical performance by Jack White.
Tom Hanks, Jon Hamm and Michael Cera are among those stopping by later in the week.