Letterman scored a 0.9 rating for the month, edging Leno, who had 0.8, among adults ages 18-49.
The Los Angeles Times said Saturday that Letterman's performance marked the first time the CBS "Late Show" had outperformed NBC's "Tonight Show" since 1994.
The Nielsen number translated to an average of 3.6 million viewers per night for Letterman and 3.5 million for his long-time rival Leno. The Times said Leno drew more than 5 million viewers in the days before Conan O'Brien's brief tenure on the "Tonight Show" with Letterman well off the pace.
The November ratings show ABC's "Jimmy Kimmel Live" having a 7-percent gain in average audience to about 2 million viewers. Letterman's gain may have spilled over to CBS' "Late Late Show" with Craig Ferguson taking over the top position in the 12:30 time slot over NBC's Jimmy Fallon.