NBC continues to be the most popular latenight choice of Americans, with Jay Leno, who’s set to exit “The Tonight Show” in just a couple of months, and Jimmy Fallon, the man who will replace him, both off to their best ratings starts in five years.

The Peacock latenight hosts have opened up considerable distance on their CBS competition and also had no problem topping ABC’s revamped lineup, which has had “Jimmy Kimmel Live” leading into “Nightline” since January.

Leno saw a boost in his final months the first time he was ready to ankle “Tonight” in 2009, but it must be encouraging for NBC to see his replacement come on so strong this fall. In fact, Fallon is now outdrawing David Letterman’s CBS show in young adults even though the latter starts an hour earlier.

Looking at the numbers for the first eight weeks of the television season (Sept. 23-Nov. 17), “Tonight” is the clear leader in the three-network weeknight battle at 11:35. Its average adults 18-49 audience of 1.11 million — a three-year high — is up 12% from last year at this time and comfortably ahead of “Jimmy Kimmel Live” (919,000, up 37% from his year-ago average when it started 25 minutes later); ABC’s lineup is seeing slight overall gains from last year in 18-49, even though “Nightline” remains down sharply in its new, later time.

CBS’ “Late Show With David Letterman” continues to struggle, with its 18-49 audience (736,000) down 20% from last year. As a result, the “Tonight Show” advantage over “Late Show” has swelled to 51% after standing at just 7% at this time a year ago.

In total viewers, “Tonight Show” is leading with 3.69 million — up 9% from last year and its best start to a season since the fall of 2008 — and is followed by “Late Show” (2.94 million, down 5%) and “Jimmy Kimmel Live” (2.60 million, up 36% from last year). Letterman is up 3% from last year in adults 50-plus, underscoring the fact that his audience is aging.

“Late Night With Jimmy Fallon” is averaging 1.93 million viewers at 12:35 a.m., up 19% from last year for a five-year high and ahead of ABC’s “Nightline” (1.66 million, down 57% from last year when it aired earlier) and CBS’ “Late Late Show With Craig Ferguson” (1.47 million, down 4%).

In 18-49, “Fallon” is up 24% (799,000 vs. 646,000), opening up a wider advantage over “Late Late Show” (480,000, down 16%).

Fallon has exhibited broad growth this fall, with gains of 20% or more in most categories and his biggest spike coming among men 35-49 (up 32%). His “Late Night” median age of 52.3 also figures to position him well opposite Kimmel (53.9 median age) and Letterman (59.1) when the three face off starting Feb. 24.

At 1:35 a.m., NBC is also doing well with “Last Call with Carson Daly,” which is up 21% in 18-49 viewers (443,000 vs. 366,000) and up 13% in total viewers (989,000 vs. 874,000).