After what seems like a pretty standard show for the first dozen songs, things get crazy early in the second set. After "Mysterious Ways," Bono asks if there's anyone near the e-stage "who can play guitar and maybe sing a little?" He spots someone on the floor holding a sign that says "singer with a broken finger" in front of his face. Of course, Bono knows that the sign-holder is Jimmy Fallon, but the crowd doesn't. Bono invites him on-stage and the crowd roars when they discover who it is. Fallon sings lead on much of "Desire" and works in some of his Bono impression moves during the song. Halfway through the song, Bono takes over the Meerkat smartphone duties from the fan who was on stage. He gives Fallon his sunglasses to wear and, when the song is over, Fallon loudly proclaims that this has been one of the best concerts he's ever seen.

Before Fallon leaves, he says he brought some friends from Philadelphia and introduces The Roots -- his houseband from The Tonight Show (and an accomplished act in their own right). Together, U2 and The Roots perform "Angel Of Harlem," reprising the collaboration they did in early May when U2 appeared on Fallon's show. Questlove takes over at Larry's drumkit on the e-stage, while Larry stands nearby singing and playing a tambourine. The crowd roars in approval and, after a round of hugs and congrats, Fallon and The Roots depart and the show continues.

A couple other changes worth mentioning: Before the show, the pre-show music in the arena is wildly different. It includes songs by Nirvana, Smashing Pumpkins and Radiohead mixed in with Joy Division, Talking Heads and other more commonly-used tunes. Also, the Stephen Hawking intro that's been used as the lead-in for "City Of Blinding Lights" (and "Miracle Drug" at a couple early shows) is moved back to its normal spot before the encore, and leads into "Beautiful Day."

There's major star power in attendance tonight. Guests include Paul McCartney, Alicia Keys, Nile Rodgers, Angelique Kidjo, Helena Christensen, Christy Turlington, Mario Batali, Steve Lillywhite, former U.S. Senator (and current presidential candidate) Rick Santorum and current U.S. Congresswoman Nita Lowey.