Barcelona have a mountain to climb on Tuesday.
Jordi Roura's men welcome a stubborn Milan side who will feel confident about shutting els Blaugrana out a second time, while the interim boss comes under serious scrutiny for his tactics and selections.
It'll be much like the first leg, except the Catalan club will hope for a rather different scoreline. How can Barca overcome the Rossoneri?
I addressed this fully in a feature after the first leg, and it remains just as critical as ever as the weeks have gone by.
Jordi Roura must introduce width to Barcelona's tactics if they are to get around this stubborn defensive Milan wall. In the first leg, his players rarely hit the byline, and in turn never made it past the last line of defenders situated on the edge of the penalty area.
Too often were els Blaugrana confined to a narrow area where their slick one-twos couldn't come off. The way to open things up is to stretch the midfielders horizontally.
Two players need to be touchline-wide at all times.
The man to bring the aforementioned width—aside from Dani Alves returning to his regular, roaming self—is Cristian Tello.
When Barcelona faced this exact issue against Chelsea under Pep Guardiola, he threw Isaac Cuenca into the deep end. This time, with Cuenca on loan at Ajax, Jordi Roura must use Tello to widen the pitch and drag Milan's midfield apart.
Fighting such a compact unit is not easy, but els Blagurana's wide pitch will stretch the triple holding pivot. If Barca can open up a yard or two of space in between, that's all Lionel Messi needs.
Speaking of Lionel Messi, he'll need to be at his very, very best if Barcelona are to overcome Milan.
Jordi Roura needs to inspire the best out of the Argentine, who despite being labeled off-colour has three goals in four games.
Messi was not at his best when Barca met Chelsea last year: The little wizard struck the post and then missed a penalty after it cannoned back off the bar. Convert those two opportunities and you're in the final.
We're likely to see Messi play in the false-nine position once more, and while his success hinges on others in part, it's arguable els Blaugrana fans need his biggest game ever.
In the 62nd minute, when Cesc Fabregas was replaced by Alexis Sanchez in the first leg at the San Siro, many a head was scratched.
After Alexis was deployed in a ghost-like No. 10 role that was vaguely further forward than Cesc's—but probably less effective—furrowed brows dominated the globe.
What is Jordi Roura doing there?
Cristian Tello, as discussed, would have been the wiser option. Even Thiago Alcantara may have been a better choice as a direct replacement for Fabregas.
Roura needs to get his subs spot on here, as the ones in Milan were arguably detrimental, not positive.
Barcelona have stuck to the very same 4-3-3 blueprint for quite some time, since it runs in the blood of the club. However, Pep Guardiola used to make specific changes in order to achieve what he called the "Eureka! moment," and Jordi Roura must start doing the same.
There's a chance the use of Cristian Tello in a 4-3-3 doesn't do what's required. If that's the case, a way to literally force his plays wider and further up the sidelines is to play a 3-4-3.
That would likely involve Sergio Busquets dropping into a defensive capacity and Andres Iniesta switching inside. Dani Alves and Jordi Alba would be squeezed up the pitch but covered for counterattacks.
That, in turn, would see Barca make ground.