In a first since he took over The Tonight Show June 1, Conan O'Brien finished second to his chief competitor on CBS, David Letterman.
The Late Show with David Letterman earned a 3.4/8 metered market household rating, compared to The Tonight Show's 2.9/7.
Jay Leno's Tonight Show regularly topped Letterman in the ratings, though O'Brien's audience likely skews younger than his predecessor.
While a single night (or even week) cannot be considered an accurate barometer of a show's ratings success, there were other factors that could have affected the late-night ratings.
NBC ran the NHL Stanley Cup finals, which ended at 8 p.m. on the west coast. As a result west coast stations ran local programming in primetime.
The Colbert Report, Comedy Central's 11:30 p.m. comedy program, is in Iraq this week taping a much hyped week of shows.
Likewise, the NBA playoffs on ABC ran late, and came down to the final few seconds, which also could have sapped some of O'Brien's viewers.
Of course, if Letterman keeps it up as the weeks move on, then it could signal a late-night ratings shift that hasn't been seen in years.