ANOTHER week, an other win for David Letterman over arch-rival Conan O’Brien.

Letterman’s “Late Show” beat O’Brien’s “Tonight Show” in total viewers last week for the fourth consecutive time — its longest winning streak over “Tonight” since 1995 (when Jay Leno hosted “Tonight”).

Letterman averaged 3.4 million viewers to O’Brien’s 2.6 million — but beat “Nightline” by only 20,000 viewers.

O’Brien, however, beat Letterman in adults 18-49 (by 34 percent) and adults 25-54 — important to NBC, which emphasizes demo numbers (read: younger viewers) over total viewers.