Jimmy Fallon's colleagues David Letterman, Jimmy Kimmel, Conan O'Brien, Craig Ferguson, and Seth Meyers were among the 11.3 million viewers who tuned in to watch Fallon take the reigns as host of "The Tonight Show" on Monday.

But Fallon's competition was fairly friendly when it came to their well-wishes and critiques of the premiere episode.

Jay Leno:

Prior to Monday's debut, Leno said of his "Tonight Show" successor: "I think he's probably the closest to Johnny [Carson] of anybody else in late night. When I watch him do, you know, a duet with Justin Timberlake or something of that nature I go, 'Well, I can't do that. I mean, I write jokes.'"

David Letterman:

During Monday's "Late Show" monologue, Letterman acknowledged the absence of his longtime late night rival, Jay Leno, by joking, "First thing this morning, I get a call from my mom. She says 'David, did something happen to Jay?' What am I gonna do?"

Letterman expressed his respect for Leno earlier this month when he said, "He was a host on 'The Tonight Show' for 22 years and now retiring. Congratulations on a wonderful run."

Craig Ferguson:

The CBS "Late Late Show" host joked during Monday's President's Day monologue that the former presidents live together in a clubhouse — as do all of the late-night hosts.

"I haven't seen Leno recently, though," Ferguson continued. "Although, one of his cars is still in the driveway, so maybe he's coming back."

When later discussing Bob Costas' return to host NBC's Olympics coverage, Ferguson joked, "I'm surprised NBC let him back. Usually when they replace a host, they stick with their decision" — referring to the Conan-Leno "Tonight Show" conflict of 2010.

Conan O'Brien:

As the only man alive who’s hosted The Tonight Show & Late Night, I want to congratulate @JimmyFallon & @SethMeyers. They’ll both do great!

— Conan O'Brien (@ConanOBrien) February 17, 2014

Seth Meyers:

Don't forget, @FallonTonight starts tonight!

— Seth Meyers (@sethmeyers) February 17, 2014

 Seth Meyers and Conan O'Brien:

Jimmy Kimmel:

congratulations @jimmyfallon - I look forward to doing this side-by-side until our suits look funny and our hair turns white #FalPals

— Jimmy Kimmel (@jimmykimmel) February 17, 2014

Daytime TV personalities weighed in:

Sending love to @JimmyFallon tonight! You don't need luck -- you've got talent. And @U2. I'll be watching. #FallonTonight

— Ellen DeGeneres (@TheEllenShow) February 17, 2014

It's CRAZY how easy they all make it look! Ok goodnight all and good luck @jimmyfallon I will watch you Mañana! Xo

— Katie Couric (@katiecouric) February 18, 2014

Congrats to @jimmyfallon and his staff for a flawless premier of @FallonTonight pic.twitter.com/cp6keB564f

— Al Roker (@alroker) February 18, 2014

There were celebrity fans:

@FallonTonight people!! That is all.

— Justin Timberlake (@jtimberlake) February 17, 2014

I simply can not host everything. Thank you @jimmyfallon for taking The Tonight Show off my plate!!! #tonight #nbc #laughmyassoff

— Hugh Jackman (@RealHughJackman) February 17, 2014

@jimmyfallon crushed it. #TonightShow #niceguysfinishfirst pic.twitter.com/0rCyxdDgpv

— James Van Der Beek (@vanderjames) February 18, 2014

And only a few haters:

Just me or does the new Tonight Show set seem tiny and the set dec cheap looking?

— Shawn Ryan (@ShawnRyanTV) February 18, 2014

See Also:

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SEE ALSO: Tina Fey, Kim Kardashian, Lady Gaga, Stephen Colbert, And More Surprise Jimmy Fallon On 'Tonight Show' Debut