Jimmy Fallon’s debut on The Tonight Show…

Jimmy Fallon’s debut as the host of NBC’s long-running The Tonight Show was a ratings hit for the US broadcaster.

Viewing-figures firm Nielsen said 11.3 million people watched him take over the show on Monday evening.

But the audience fell short of the 14.6 million viewers who saw Jay Leno sign off as host of the programme.

The figures do not necessarily take account of those who watched segments of the show online via services such as YouTube or Hulu.

Fallon, 39, will compete against late-night shows hosted by David Letterman on CBS and Jimmy Kimmel on ABC. Kimmel, 46, has proved popular with the key 18-49 demographic.

“I really don’t know how I got here,” Brooklyn-born Fallon, who rose to fame as a cast member on the US comedy show Saturday Night Live, told Monday night’s cheering studio audience.

“I just want to do the best I can, and take care of the show for a while. If you guys let me stick around long enough, maybe I’ll get the hang of it.”

Fallon’s guests included a parade of celebrities such as Robert De Niro, Will Smith, Lady Gaga and Mike Tyson, plus a performance from the rock band U2.

Leno stepped down for a second time as host of the six-decades-old show on 6 February. He originally took over from Johnny Carson in 1992.

Leno briefly retired in 2009, handing over to comedian Conan O’Brien.

But Leno came back when O’Brien quit amid an attempt by channel executives to reschedule The Tonight Show to later in the evening.

Fallon’s debut, coming after the broadcaster’s nightly Olympics programme, gained two million more watchers than O’Brien’s debut.