The result kept Mazzarri's men winless in 2014 and saw them drop to sixth in the standings, and left the boss full of admiration for the victors.
"We needed to focus on every little detail with great determination, the way Juventus did," Mazzarri said to Sky Italia.
"When the going gets tough, Juve get going.
"Juve were more determined and aggressive, whereas we were sluggish and lazy.
"I was annoyed at the way we conceded the second goal, as we could have cleared the danger and we were simply too slow.
"Juventus were quicker to the ball.
"Unfortunately, we have a lot to learn."
Inter again struggled in front of goal, much to Mazzarri's frustration.
"We created chances," he said. "We cannot forget that (Inter's top scorer) Rodrigo Palacio twice could have made it 3-2 and reopen the game."
Inter have won just one of their last 10 league games and sit two points behind fifth-placed Hellas Verona, who hold the last Europa League qualifying spot.
However, Mazzarri is not ready to give up on his team's season just yet.
"I have faith," said the 52-year-old, whose side next face Sassuolo at the San Siro on Sunday night.
"We've got the right attitude, tactical approach and the younger players are growing.
"It's just a pity that results are not coming our way.
"As I said in the past, this is a year of growth and evaluation.
"We just need a victory to turn things around - that is all."