A female fan is wearing an 'Edge Girl' slogan on her t-shirt tonight. A sign from another fan reads, Larry Rocks.
These are not the only firsts in Chicago. Tonight we have the first Elevation 2001 outings for both 11 o'clock Tick Tock and Out of Control, still thrilling after all these years.
In fact Out of Control is so special that the band can't recall playing it live for the best part of two decades. And as for special guests, tonight we have an extra special guest, the son of Burmese pro-democracy leader Aung San Suu Kyi.
Meanwhile, a fan apparently fingered by the nimble-fingered vocalist at Saturday's show, is desperately seeking shades. 'Please can I have my glasses back Bono?' reads the sign, while another says 'Bono, did you find what you were looking for?'. Doubtless someone else did - their sign reads, 'My first U2 Concert'
Edge is wearing his No. 21 t-shirt tonight, but in a subtle sartorial variation, it's a black T, not the customary red. Beautiful Day offers a special lyrical nod to the Windy City ('Love this town, Chicago') which perhaps explains the energy tonight.
'This is our first single on Island Records,' explains Bono, as the band start up '11 o'clock Tick Tock'. Edge's guitar seems to be out of tune so they do a double-take.
'This is our second single on Island Records.' Same problem, another false start. 'I'm not sure my heart could take that twice.' Third time lucky and the song goes down a storm.
And to another debut. From 'our first single on Island Records' to 'our very first single'. This, apparently, is a surprise to Edge, who later reveals that he had been expecting the song to be in the final Chicago performance - they haven't played it in 20 years. Still no-one extemporises like Edge.
Soon Bono is introducing Adam and Larry to the good people of Chicago, most of whom seem to have extensive previous knowledge.
'This is a song that Joey Ramone transformed,' says the vocalist as In A Little While is introduced. 'A lovely song and he turned it from a song about a hangover into a gospel song, well that's all I'm hearing now when I hear this song.'
As Edge sings the last line, the guitarist and singer clasp hands and embrace.
'So any punk rock groups or any kind of bands or DJ's or anyone stuck on the trail that might take you 20 years later to a city like Chicago...' Desire is for all of them.
And then a longer than usual introduction to Stay from Bono, recalling a night long ago just after it was time to dream it all up again and just before the Baby was born.
'Berlin, it was very, very fucking cold there when we wrote this song and a couple of others at Hansa Studios by the wall.
'We came into Berlin when the wall was coming down and there was a party to celebrate the unification of Germany. We were on the last flight into Berlin, we had the skies to ourselves and the captain said over the loud speaker, 'We're the last flight into Berlin and we're going to take you on a tour of the town.
'We flew over Berlin and we thought this is a bombs away situation but we were happy. They were throwing a party for the celebration but everyone looked like they were having a crap time. We realised we came to the party that was protesting the pulling down of the wall..'
Stay closes with 'London, Belfast, Chicago' before Bad opens up and Mysterious Ways is here with a lyrical nod to travelling companion P J Harvey as Bono sings ' Lick my legs, I'm on fire.' (Expect fan signs shortly reading, 'Bono, my tongue is yours' and 'Will lick your legs anytime.')
'What does that sign say ?' asks Bono as The Fly begins. 'You want to dance with my wife, I don't dance, I dance for my life...' whereupon The Fly tears the United Center apart and Bono rips his shirt up, pressing himself against the video screens and singing 'Goodbye, goodbye' until the end of the song.
'Thanks for coming out and thanks for giving us a great life,' he says after Pride (In The Name of Love) and before One. 'Thanks to PJ Harvey, thank you for following us down the Jubilee trail. There's a lot that 18,000 people can do if they put their minds to it.'
There's a lot that just one can do. Walk On is dedicated to Aung San Suu Kyi, under house arrest in Burma. Her son, here tonight, will doubtless pass on the message.