Vendors outside the Cathedral sold pins, calendars and posters with the image of Francis. The flag of the Vatican City seemed to be the most popular sales item.
Uma Eiras, a 10-year-old student, waved a tiny one with its two white-and-gold vertical bands and said she would hang it in her room.
There seemed not to be a single pew empty inside the giant national Cathedral and many followed the Mass on large screens across the street.
Sabina Podrez, a 39-year-old scrivener, said she attended the Mass out of hope that Argentina and the world will change under a new pope.
"We were going to work disheartened, with insecurity," Podrez said. "This is a breath of fresh air."