Ruslan Malinovskyi's deflected shot off Alex Sandro proved decisive at the 87th minute in Bergamo.
“It was a good game against a strong team. We played the match we needed to, then they were lucky with the late goal, but we played with great determination and aggression. It's disappointing, we could've brought home at least a point," Pirlo told Sky Italia.
Despite the defeat, Pirlo was impressed with the Juventus performance.
“We have not faced all our games with the same attitude and determination. It's a completely different team when we have those elements, but despite me pointing it out, we have dropped too many points by not having the right attitude in the smaller fixtures.
“We knew Atalanta would make it a duel all over the field, so that's how we prepared it. We kept good possession, covered the spaces, Atalanta can force you to play differently to other situations, but we did well."