According to Nielsen Media Research, “Late Show with David Letterman” averaged 3.68 million viewers and “The Tonight Show with Conan O’Brien” averaged 2.82 million viewers last week, which means Letterman beat O’Brien by almost 800,000 viewers.

In fact, Dave has won two of the past three weeks among all viewers during which both shows aired original programs.

So why the sudden gains? In addition to “Late Show” landing guests like Paul McCartney, a generation gap is emerging, with the median age of O’Brien’s audience more than 10 years younger than Letterman’s last week.

A large number of traditional “Tonight Show” viewers are flocking to “Late Night” because, as CBS’ chief researcher David Poltrack puts it, “they’re realizing this isn’t the ‘Tonight Show’ anymore. It isn’t what I’m used to.”

Even though O’Brien’s numbers are down, NBC execs couldn’t be happier with the generation gap.

“The business we’re in is selling viewers in the 18- to 49-year-old age group to advertisers, and Conan is doing very well by that measure,” NBC’s top late-night exec said. “In fact, he’s doubling the competition in the younger half of that group. It’s going to take months and years for the ultimate ratings tale to be told but so far, we’re very pleased at how younger viewers are clearly shifting to Conan.”

Stay tuned.

Friday, July 17
Tracey Ullman – “The Hour with George Stroumboulopoulos” – rerun
Michael Buble, Brad Wollack, Whitney Cummings – “Chelsea Lately” – rerun
Brent Butt, Susie Essman, Mark McKinney, Craig Ferguson – “The Hour with George Stroumboulopoulos” – rerun
Gavin Rossdale – “The Bonnie Hunt Show” – rerun
Tommy Johnagin, Metric – “Late Show with David Letterman”
Demi Lovato – “The Tonight Show with Conan O’Brien”
The Dead Weather – “Late Night with Jimmy Fallon”
Daughtry – “Jimmy Kimmel Live!”
Ray LaMontagne – “Late Late Show with Craig Ferguson”
Chris Cornell – “Last Call with Carson Daly” – rerun

Saturday, July 18
The Oak Ridge Boys – CBS “Early Show”
Lucinda Williams, Old Crow Medicine Show – “Austin City Limits” – rerun
Duffy – “Saturday Night Live” – rerun

Sunday, July 19
Pete Seeger – CBS News “Sunday Morning”

Monday, July 20
Alanis Morissette – “Live with Regis and Kelly”
Flo Rida – “The Ellen DeGeneres Show” – rerun
Prince – “The Tavis Smiley Show” – rerun
David Byrne – “The Hour with George Stroumboulopoulos” – rerun
Tallan Latz – “The Bonnie Hunt Show” – rerun
Jeff Altman, Spinnerette – “Late Show with David Letterman”
Kate Voegele – “The Tonight Show with Conan O’Brien”
Tom Jones – “Late Night with Jimmy Fallon”
Linkin Park – “Jimmy Kimmel Live!” – rerun
Margaret Cho, Eric Church – “Late Late Show with Craig Ferguson”
Kelly Osbourne, Ben Harper & Relentless 7 – “Last Call with Carson Daly” – rerun