Ciro Immobile's penalty proved the difference in the first leg of the last 16 tie in Rome.
"In the first half, we had to take the lead. We had three clear chances. We have to do these things," Tuchel told DAZN.
The second half was "characterised by uncertainty again", he said. "It was a bit slapstick."
Bayern were hamstrung by the dismissal of Dayot Upamecano, who was shown a red card for crashing into Gustav Isaksen in the penalty area.
Immobile stepped up to score the resulting spot-kick.
"We made a lot of individual mistakes and we conceded a penalty and red card from out of absolutely nothing," Tuchel said in the post-match press conference.
"With the performance we did everything to lose this game, which was completely in our hands."
The defeat in Rome follows the 3-0 reverse against Bayer Leverkusen which leaves Bayern five points off the pace in the Bundesliga title race.
But asked if he feared for his job, Tuchel said simply: "No"
