The Bianconeri crashed out of the Champions League in the Round of 16, despite the fact Porto were down to 10 men from the 54th minute.
Even in extra time, they were only able to scrape a 3-2 win on the night, going out on away goals, 4-4 on aggregate.
“When you make four big errors over two legs in the Champions League Round of 16, you can get eliminated," Pirlo told Sky Italia.
“We didn't get it wrong when Porto were down to 10, as all we could do was try to spread them out by moving the ball side to side and packing the penalty area with bodies. That is how the goals arrived.
“It will take a few days to cancel this game from our minds, but then we must face every game with the right attitude, realise we're still only in March and have time to climb the Serie A table."
Pirlo also defended their slow start to the game.
“We had started well and there was a chance with Alvaro Morata to take the lead immediately. It didn't go in, there was an error for the penalty, we could've conceded a second, but then played the game we should've done in the second half, helped also by the extra man.
“I don't think our starts are a problem. We knew Porto would play like this, the game could change if we scored in the opening minutes. When you concede, then it becomes a completely different match."
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