"To be honest, perhaps the atmosphere before the game made it seem like an easy match and there weren't many people there," said Mancini after his side fought back from 2-0 down to win 4-2.
"The second goal in particular woke us up. We knew it was a tough encounter, as they have such good forwards, but it took two goals to shake us out of that stasis.
"We were a little too soft on the ball and going 2-0 down gave us the stimulation we needed to get into the game, so in the end that start proved to be a blessing in disguise."
CSKA Moscow had just one point in three games, but were aggressive from the start and took a 2-0 lead through Jo and Vagner Love.
"It's not that we underestimated CSKA, it was the atmosphere at San Siro before kick-off. It did not give us the right approach," insisted Mancini.
Zlatan Ibrahimovic and Esteban Cambiasso grabbed a brace apiece to turn the tie around and keep Inter on top of their Champions League group.
"Ibra's second goal was fantastic, but so was Cambiasso's on the Hernan Crespo dummy. It was an entertaining match in the end!"