The Nerazzurri were comfortably beaten at the Juventus Stadium, and Mazzarri was upset at the "lazy" performance from his players.
"I was annoyed at the way we conceded the second goal, as we had the opportunities to clear it and were too sluggish. Juventus were quicker to the ball, more aggressive and that made the difference," he told Sky Sport Italia.
"We need to focus on every little detail with great determination, the way Juventus do. When the going gets tough, they get going. Juve were more determined and aggressive, whereas we were sluggish and lazy.
"We created chances and let's not forget Rodrigo Palacio twice could've made it 3-2 to end with a siege on their goal."
Inter have now gone six games without a victory and have won just once in their past 10 league fixtures.