Watch U2 Enlist Jimmy Fallon, the Roots for Surprise MSG Appearance

'Tonight Show' host sang "Desire" at Madison Square Garden, while the Roots joined on "Angel of Harlem"

A few hours before U2 took the stage for their third night at Madison Square Garden, the band's longtime producer Steve Lillywhite sent fans into a tizzy with a single Tweet: "Was at U2 soundcheck today," he wrote, "and all I can say is, everyone who goes tonight will get a good surprise!!" Rumors began flying that Bruce Springsteen was going to join the band at some point, though once the show began, things shifted a bit when Paul McCartney was spotted on the floor. Anything seemed possible. 

The first surprise guest revealed himself after "Mysterious Ways" when Bono brought a man onstage holding a sign that said "singer with a broken finger." The place went nuts when they realized it was Jimmy Fallon. "I'm a big fan of Irish people that fall down and hurt themselves," Fallon said. "So you're like a mentor to me, brother. Edge, what you did a couple of weeks ago falling off the stage was classic, brother. I'm happy to be a part of the club." He then took the mic and did his best Bono impression on "Desire," down to the little grunt that kicks off the song. 

"I brought a few friends of mine," Fallon said after the song. "I'd like to introduce them. You know them from Philadelphia. The Roots, ladies and gentlemen!" Questlove and company then marched into the E stage and joined U2 on "Angel of Harlem," a track they played together on The Tonight Show in May. Larry Mullen Jr. even gave up his dream kit to Questlove, playing the tambourine instead.

U2 were originally slated to appear on The Tonight Show for a full week last November, but were forced to cancel after Bono's devastating bike accident the evening before the first show. Fallon and The Roots played "Desire" in their place one night, and in May, the fully healed band came onto the show and played a surprise set at the Grand Central Station subway station.

Alicia Keys, Nile Rodgers, Angelique Kidjo, Helena Christensen, Christy Turlington and Mario Batali were also in the audience at last night's MSG gig. Former US Senator and current presidential candidate Rick Santorum stopped by before the show and got a photo with Bono, but left before the music began to appear on The Rachel Maddow show. Fans that hoped to see McCartney get onstage had to make do with a snippet of "All You Need Is Love" at the end of "One."