For the third season running, “Nightline” was the #1 show in late night topping NBC’s “The Tonight Show” and CBS’s “The Late Show.” But as “Nightline” prepares for a late night shift, the show will likely see a drop-off in viewership with the hope of staying #1 against Jimmy Fallon on NBC and Craig Ferguson on CBS.

“Nightline” topped “The Tonight Show” with its largest A25-54 lead (+45,000) in 17 years – since the 1994-95 season. “Nightline” beat “The Late Show” by its largest margins in both Total Viewers (+728,000) and Adults 25-54 (+186,000) in 13 years – since the 1998-99 season.

In January, “Nightline” will move to 12:35pmET/11:35pmCT as “Jimmy Kimmel Live” gets the coveted timeslot after the late local news, going head-to-head with Jay Leno and David Letterman.

While “Nightline” gets the win, the show is down from the 2010-2011 season: down -6% in Total Viewers and -10% in both A25-54 and A18-49 viewers. But “Nightline” is not alone in seeing a drop-off. Collectively, year-over-year “Nightline,” Leno and Letterman are down -7% in total viewers and down -12% in both the A25-54 and A18-49 demos as cable programs and other media vie for consumer attention, especially among younger viewers. And the loss of younger viewers is not an anomaly: the shows are down -13% (A25-54) and -19% (A18-49) vs. the 2009-2010 season.

ABC’s ratings are based on a 25-minute broadcast, while CBS and NBC are based on approximately :50 minutes (prior to the final national commercial break of each program).

• Averages for the 2011-2012 Season:
  

The numbers for the week of Sept. 17 and the third quarter of 2012 show the downward trend as all three shows are down from their season averages. Not a good sign and likely another factor in ABC’s decision to move Kimmel up a half hour.

• Averages for the week of Sept. 17, 2012:
  

• Averages for Q3 2012: