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Deeper into the mire for Thomas Tuchel. Defensive possession might have proven to be an effective tool for the head coach to achieve great things in this competition but the 2021 champion learned the most telling of lessons in the Eternal City. His approach only works if you can trust your defense.

Dayot Upamecano has proven often enough in his career that he is not the sort of center back who can reliably deliver 90 blemishless minutes. Those are the sort of defenders that Tuchel forged into an elite unit when he won this competition with Chelsea. Eleven months in, there are precious little signs that he is doing that with Bayern. The pedestrian pace with which the visitors looked to grind Lazio down might have been effective if it was not paired with a backline that was all too easy to punch through on the counter. That was not the title-winning formula three years ago. It certainly isn't now.

Tuchel didn't make the challenge that proved to be the decisive factor in the Stadio Olimpico. It was Upamecano who rashly stuck a boot on the ankle of Gustav Isaksen when all he needed to do was stay big and show the Dane towards the byline. You could proffer the same explanations on Saturday night after what felt like the epochal defeat to Bayer Leverkusen. Tuchel was not one of the seven defenders falling asleep when the Bundesliga leaders took a quick throw.

When Bayern's title challenge at home and on the continent begins to fizzle out because of these individual errors, however, Tuchel can rest assured that he will carry the can. There is fair reason why that might be the case on Wednesday. He might not have handed Ciro Immobile the penalty from which he won this first leg but Tuchel set his side up in such a way that they were vulnerable to one moment of Lazio brilliance or their own madness.

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Defensive possession might be an effective weapon in this competition but even the most cautious of build-ups has to have an end point in mind. Too often Bayern meandered to nowhere in particular, everyone in black and purple insistent on carrying the ball infield where three lines of Lazio blue were waiting for them. When the Bavarians stretched the ball from one flank to another, they posed a serious test. As early as the sixth minute, Leon Goretzka probed the space on the left with a quick switch. Leroy Sane had drifted across to force an overfield, dovetailing with Jamal Musiala, he made space for Joshua Kimmich to take a touch and hang one to the back post. Thomas Muller flicked a header across, Harry Kane couldn't quite tuck it away. More of that, you would think, and the match, perhaps even the tie, would be Bayern's. 

Instead, they slowly wound their way towards zero shots on target, rarely looking up and aiming at the goal but instead turning towards Manuel Neuer, looking for the safe option. Was this a reaction to their slapdash performance in Leverkusen at the weekend, a reluctance to be ripped to shreds on the counter as they were by Alejandro Grimaldo et al? Perhaps, but it could just as easily have been an attempt by Tuchel to ape his past European successes, a surprise triumph for conservatism on a par with the 2019 British election.

Passes made by Bayern Munich in Lazio's half during their 1-0 defeat in Rome TruMedia

What seems so curious about Bayern tonight is that no one could accuse them of similar caution when in Bundesliga action. Even if you factor in the notable weirdness of Germany's top flight this season, Tuchel's side has been blowing out the rest of the continent in terms of attacking threat. In three fewer games than the likes of Barcelona, Liverpool and Arsenal, the Bavarians have put up five percent more expected goals. Injuries might have dulled their threat out wide but a front four of Kane, Sane, Musiala and Muller really should have enough threat to test an upper-midtable Italian side.

Credit for Bayern's travails certainly should go to Maurizio Sarri, not exactly a coach known for carefully-applied pragmatism. Still, he had a better reading of Tuchel's side than his opposite numbers, concluding that they would gravitate towards the center of the field, where he could pack bodies and wait to spring on the break. It is one thing to have that gameplan, and another to get the likes of Felipe Anderson to execute it. He typified the remarkable excellence of a side who probably would not have made it this far if they hadn't got such a favorable group stage draw.

They probed holes in the Bayern backline that Tuchel's best sides would never have allowed to emerge. Isaksen, in particular, had great joy slipping into the space vacated by fullbacks who did not offer anywhere near enough going forward to mitigate their difficulties at the other end. It did not take intricately crafted moves to break through, just one pass over the top. Bayern would do the rest for them.

Tuchel could have negated that soft underbelly. He has spent so much of his reign complaining about the absence of a true destroyer in midfield, why not embrace the qualities of the Kimmich-Goretzka tandem and take the game to their opponent? Cup competitions might be a more effective format for the best defenses to shine through but Bayern don't have one of those. What they do have is some of Europe's best forwards but even they will look ordinary in the extreme if they're waiting an age for a pass towards the penalty area.

While Bayern might believe they have an inordinate amount of it with which to build their attacks, time is not as precious a resource for Tuchel now. Perhaps he could survive Leverkusen breaking his club's strangle over the Bundesliga if they do so with the style they showed on Saturday. Couple a failed title defense with an exit at the Allianz Arena next month, however, and it would be a bold man who predicted his employment by Bayern next year.