08/23/2009 05:12 am ET | Updated May 25, 2011

"Nightline" Wins 4th Week In A Row, Letterman Tops "Tonight" For Second Straight Week

The week of July 13 turned out to be something of a historic one for late night TV, as both "Nightline" and "The Late Show with David Letterman" achieved ratings they hadn't reached since the 1990s.

"Nightline" enjoyed its fourth consecutive week with the most total viewers for the first time since 1995. It averaged 3.743 million total viewers, ahead of Letterman's 3.454 million and 2.713 million for "The Tonight Show." "Nightline" grew 21% in total viewership over last year's mark for this week.

"The Late Show" beat Conan O'Brien's "Tonight Show" for the second straight week for the first time since 1998. "The Tonight Show" also experienced its lowest total viewer ratings since 1991/1992 and lost to "Nightline" in the Adults 25-54 demographic, which is considered a strength for O'Brien.

CBS beat NBC in the 12:30 AM slot as well, with "The Late Late Show with Craig Ferguson" beating "Late Night with Jimmy Fallon," 1.478 million to 1.269 million, the largest margin since Fallon took over as host in March.