Disciplined Lazio stifled the German side's attacks and Bayern were toothless throughout, failing to get a single effort on target in the match.
Ciro Immobile scored a 69th-minute penalty to earn hosts Lazio a 1-0 victory over 10-man Bayern Munich on Wednesday in their Champions League round of 16 first-leg clash.
Immobile converted his spot-kick after Bayern defender Dayot Upamecano's clumsy challenge on Gustav Isaksen for which the France international was sent off with a straight red card.
Disciplined Lazio stifled the German side's attacks and Bayern were toothless throughout, failing to get a single effort on target in the match.
The Bavarians, favourites going into the game, were desperate to bounce back from Saturday's 3-0 Bundesliga loss to leaders Bayer Leverkusen which left them five points off the top.
They will return to Munich with more pressure piling on coach Thomas Tuchel and his team after their second straight defeat. They have failed to score in their last two games.
"We started well had a chance in the first minute and then with Harry Kane and then with Jamal Musiala. We had the game under control in the first half," Tuchel said.
"But in the second our performance dropped inexplicably. We made too many individual errors and made our opponents stronger and we lost concentration. We lost our rhythm.
"It was completely our responsibility. We lost a game today that in the first half looked like we could not lose it."
Tuchel played down concerns about his situation.
"Worried about my future? No, I am not," he said.
Bayern created early chances for Joshua Kimmich and Harry Kane, who both narrowly missed the target.
The Italians, who lost 6-2 on aggregate to Bayern at this stage of the competition three years ago, responded with a fierce Luis Alberto strike that flew wide of Manuel Neuer's goal.
The tempo gradually dropped, Bayern struggled with the disciplined Italian back line and had to wait until the 40th minute to threaten again when Musiala fired over the bar from close range.
Lazio should have taken the lead two minutes after the restart when Isaksen only had Neuer to beat but the keeper stood his ground to block his shot.
The Dane won a penalty when Immobile passed to Isaksen in the box and Upamecano arrived late and stepped on his ankle.
Immobile kept his cool and sent Neuer the wrong way to give Maurizio Sarri's team the advantage going into the return leg in Munich on March 5.
"We worked and prepared for this match to have a say in it," said Immobile. "I was convinced that the team would put everything out there.
"We had some opportunities and we had to be good at exploiting them ahead of the return match and we did just that."
Meanwhile, second half goals from Kylian Mbappe and Bradley Barcola secured Paris St Germain (PSG) a hard-fought 2-0 win over visitors Real Sociedad in the first leg of their last-16 Champions League tie on Wednesday.
The Basque club, who arrived at the Parc des Princes unbeaten in this year's competition after topping Group D, were arguably the better side until Mbappe fired home a volley after he pounced onto Marquinhos' corner to give PSG the lead in the 58th minute.
PSG took control of the game and in the 70th minute, Barcola extended their lead as he nudged the ball through the legs of the goalkeeper Alex Remiro.
"We struggled a lot in the first half. We spoke to each other at halftime and the coach (Luis Enrique) pulled our strings. He was really upset," PSG captain Marquinhos told Canal Plus.
"Our attitude was much better in the second half. He (Luis Enrique) always tells us the truth, and that's very important for the team.
"He gave us some advice ... and that worked well in the second half. The first part of our objective has been achieved. It's important to win at home."
PSG were lucky to go into the break with the match scoreless as Real Sociedad’s captain Mikel Merino unleashed a thunderous strike that exploded off the crossbar just before halftime.
A resilient Mbappe, who missed his club's previous match due to an ankle injury, took advantage of Real Sociedad being temporarily down to 10-men after defender Hamari Traore was on the sidelines receiving medical treatment.
Paris St Germain's Kylian Mbappe (L) attempts to score a goal against Real Sociedad at Parc des Princes Stadium in Paris, France on February 14, 2024. PHOTO | REUTERS
Mbappe's strike into the the top corner sparked wild celebrations among the Parc des Princes crowd and the Frenchman almost extended PSG’s lead a little later, but his thunderous effort was tipped away by Remiro.
Barcola extended PSG’s lead in the 70th minute with a fine individual display as he burst through from the halfway line to net a tidy finish.
PSG had more chances to score but the visitors held on and will have a tough task to fight back from two goals down in the return leg in Spain on March 5.