I called it. I knew it won't be an easy game for Arsenal, they were the favourite but should be lucky to earn even that 1 point. The major credit for that goes to Arsenal's goalkeeper, Raya who made a fantastic double save of Retegui's penalty. Retegui should've done better on that rebound, he seemed to have enough time to take a better aim with that header, but it went right in the middle of the goal, making it possible for Raya to save it.
Apparently it was Atalanta's first ever goalless draw in their Champion's League history. What's a bit strange, it's Arsenal's 3rd away Champion's League game in a row, when they failed to score a goal.