In his first live “Late Show” broadcast since the start of the Republican National Convention, Stephen Colbert promised the return of an old friend from his basic-cable days, but instead, viewers got to see two familiar faces: first, Jon Stewart, the longtime host of “The Daily Show,” and then “Stephen Colbert,” the unctuous conservative commentator that Mr. Colbert portrayed for nearly a decade on his Comedy Central program, “The Colbert Report.”

The guest appearances from Mr. Stewart and that other Mr. Colbert appear to have paid off for “The Late Show.” According to preliminary ratings information on Tuesday, “The Late Show” was the No. 1 broadcast late-night show in overall viewership on Monday night, the first time the program has surpassed all its competitors (including Jimmy Fallon’s “Tonight” show on NBC and “Jimmy Kimmel Live” on ABC) since Feb. 15.

“The Late Show” announced in June that it would present two weeks of live broadcasts, Monday through Thursday, to air after each night of the Republican and Democratic conventions. Though the current iteration of the program made its debut to considerable fanfare in September, it has had trouble finding a consistent voice under Mr. Colbert, who succeeded David Letterman as host and who has tried to expand his horizons beyond the irreverent political comedy he performed on “The Colbert Report.”