Juventus were left with a mountain to climb after in-form Bayern Munich claimed a 2-0 advantage in their quarter final first leg - the opener coming inside the first 30 seconds.
Uefa Champions League: Apologies from Pirlo as early blunder puts Bayern in control
The Italian, a key part of Juventus' revival over the last 18 months, looked a shadow of his normal self after his error handed the in-form Bundesliga leaders a goal inside the first minute.
"I'm sorry I made so many mistakes but we still have a return match," the former AC Milan man said afterwards.
"We will analyse this defeat and draw some conclusions.
"Bayern have shown today that they are a stronger team than us."
Pirlo gave the ball away to Bastian Schweinsteiger as he tried to play his way out of defence inside the first 30 seconds of the match, with Austrian youngster David Alaba picking up the ball from 30 yards out to hammer home.
Arjen Robben, having replaced the injured Toni Kroos early in the first half, almost marked his introduction with a goal in the 18th minute only to be denied by a fine save from Gianluigi Buffon.
Franck Ribery then saw a shot deflected into the side-netting before Robben fired another great opening wide just after the half-hour.
Robben drew another save from Buffon in the 35th minute, albeit a comfortable one, before Schweinsteiger fired a half-chance over the bar.
Juve's best hope of success looked to be from Pirlo's set pieces and they almost drew level from one on the stroke of half-time, Leonardo Bonucci glancing a header just over from the veteran playmaker's inswinging corner.
That effort, and the half-time interval, offered some respite to Juve but they were back on the defensive at the start of the second half, with Buffon denying Mario Mandzukic at his near post before then flying to his left to parry an Alaba free kick.
Bayern were employing a shoot-on-sight policy and another effort from outside the box led to their second goal in the 63rd minute.
Buffon kept out Luiz Gustavo's shot but the rebound was picked up by Mandzukic and he laid the ball back into the centre for Muller to tap into an empty net.
The goalkeeper produced a superb one-handed save to deny Muller in the 90th minute and, with the Germany international firing the rebound over with the goal at his mercy, that could yet prove decisive in the second leg.
"We made our game prevail as planned and we took Pirlo out of the game, we succeeded in doing that," said Jupp Heynckes, the Bayern coach, afterwards.
"I must pay my team a big compliment for that."
Kroos looked to have suffered a muscle tear during the match, with Heynckes admitting it would 'take a long time' for the player to be ready to return.
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