Nielsen company figures released Tuesday show 11.3 million people tuned in to watch Fallon's New York debut on Monday night.
It was the second-biggest audience for "Tonight" since May 2009, when Jay Leno stepped down for Conan O'Brien's brief run as host.
Fallon's "Tonight" debut fell short of the 14.6 million who tuned in Feb. 6 to see Leno sign off, again, after 22 years as host in Burbank.
Enjoying a post-Winter Olympics time slot, Fallon drew 2 million-plus viewers more than O'Brien's June 2009 "Tonight" opening audience of nearly 9.2 million.
NBC says Fallon's "Tonight" debut, with guests Will Smith and U2, was up 71 percent over his Feb. 6 "Late Night" farewell's audience of 6.6 million,