It's one of the biggest events on US TV this year. Jimmy Fallon handily took the gold medal for non-Olympic TV viewing on Monday when he made his debut as host of The Tonight Show, succeeding Jay Leno.
Twenty per cent of US households watching TV at midnight tuned in to Fallon, according to preliminary Nielsen ratings data shared by NBC on Tuesday.
Network NBC said the show drew 11.3 million viewers, which is short of the 14.6 million who tuned in to see Fallon's predecessor Leno sign-off after 22 years helming the program.
NBC said the show – which started a half-hour later than usual due to Winter Olympics coverage – was "easily the number-one non-Olympic telecast" on Monday, as well as the evening's dominant late-night program.
Trailing well behind were CBS's The Late Show with David Letterman and ABC's Jimmy Kimmel Live, each with 5 per cent of households tuned in.
Leno, 63, signed off from The Tonight Show after 22 years on February 6 as NBC relocated the show from Los Angeles to New York and put Fallon, 39, in the host's chair in a bid to attract a younger, hipper demographic.
"I really don't know how I got here," said Fallon to a cheering studio audience after passing through a blue curtain to take the reins of one of the greatest franchises in American television.
"I just want to do the best I can, and take care of the show for a while," he added.
"If you guys let me stick around long enough, maybe I'll get the hang of it."
His guests on Monday night's show included Will Smith and U2, the latter performing atop Rockefeller Center, plus a parade of other celebrities including Lady Gaga, Lindsay Lohan, Mike Tyson, and Robert De Niro who paid back mock $US100 bets that Fallon would never host the show.