Barcelona ensured their Champions League dream remained on track this week with a strong—but not necessarily convincing—win over AC Milan at Camp Nou.
A brace from Lionel Messi helped the home team overcome the Rossoneri, who had caused them serious problems in the knockout stage last season, and while the scoreline might have read that La Blaugrana walked away with an easy victory, the result was far from easy for Barcelona.
Milan definitely threatened; they simply didn't have the finished product.
Let's break down the film and see what went so right for Barcelona, what went so wrong and why Milan couldn't finish with a better result than they did.

The Return of Lionel Messi
 
Having come into this fixture in the middle of a "goalscoring drought" (at least by his high standards), Messi proved in this one just how deadly he can be.
Truth be told: He was always this deadly, but we all needed reminding. And while the two goals that he scored might have been the convincing point for many people, it was his movement and willingness to drop back that completely undid Milan—much like when they met last season.
 
In 2012, it was David Villa ahead of him on the field, occupying defenders and making space for Messi to drop back into midfield and build the attack alongside Andres Iniesta. This time it was Neymar, but the final product was no less overpowering from La Blaugrana.
What Messi did here—and what he continues to do—is move.
His timing and knowledge of when to drop back are like no other, and it rarely matters how many defenders an opponent tries to get behind the ball to stop him. If it's not him, it'll be someone else. He has the creative skills and talents to pick off a fellow attacker if needed, but he also has the close control and dribbling talents to waltz through even the most compact defenses.
Understanding his movement is simple: It's out and then in.
Look at the image below. Messi has just dropped back to find himself ahead of the flat back four from AC Milan and into the channel between defense and midfield.
Most strikers would stay there, thinking that they've found enough space.
Yet Messi continues to drop back even further, and as the image below shows, he is quickly ahead of the central midfielders, ready to receive the ball and launch an attack. No defender has picked up his run because it's, well, backward, and no central midfielder has picked him up either because they don't want to jump out of the defensive line they've worked so hard to establish.
In the example below, Messi picks up the ball, works it into the box and almost creates a goal out of nothing. Earlier in the game, he floated a pass for Neymar's penalty.
And later on in the game, he executed the exact same move.
Cesc Fabregas picked up the ball in central midfield and, with limited options ahead of him, held the ball up for a moment. Messi dropped back between two very flat defensive lines (illustrated here with the blue boxes) to receive the pass and try and work an opening.
Out to receive the pass, in to Fabregas and goal. It was as simple as that.
 
Milan—like most teams would—struggled to restrict this part of Messi's game because there is no real way to play against it. Teams can't stick a central defender on him because he moves too freely; placing a defender on him would simply pull that defender from the back line.
You can't place a midfielder on him, either, because not only does he drop back, but he also sits on the last man at times, looking for a through ball or pass.
Defenders thought they had the better of Messi (and Barcelona's tiki-taka in general) when they started to drop everyone back behind the ball, like Chelsea did in the Champions League semifinal. The "parking the bus" technique for those more familiar with that term, but now, with his sublime movement, Messi has again managed to find space.

He's moved back to where the midfielders were originally.
And for the most part, it's proving to be a wonderfully successful tactic.
Time for defenses to adjust, again.
 
Milan Re-Expose Barcelona's Wide Weakness, but No Result
 
Despite being largely outplayed on the scoreboard by Barcelona, Milan actually weren't all that bad.
It's hard for a team to show its collective worth when playing Barcelona at the Camp Nou, considering you only have about a fourth of the match to actually have the ball. Despite the constant stream of criticism which has pelted the club from every direction, there were a few other positives to take away from the match. Kaka is back, and he continues to be Milan's player of the match every time he plays.
He's 100 percent correct in finding the positives.
As crazy as it might seem looking at the postgame statistics, the Rossoneri were actually very strong in patches (particularly the 20 minutes following half-time), and had a little bit of luck fallen their way with one of Mario Balotelli's chances, they might well have finished with a different result than the 3-1 loss they were ultimately dealt by the home team.
Perhaps the biggest positive for Milan here was their use of the flanks, which quickly exposed Barcelona's weakness against width at the back.
 
When Milan stunned Barcelona 2-0 at the San Siro last year, they did it on the back of swift counterattacks down either flank. Stephan El Shaarawy and Kevin Prince-Boateng caused problems for La Blaugrana with their free running and ability to get in behind defenders, and for the most part, that was a huge problem for the home team again in this fixture.
It wasn't as evident in the first half (when Milan were in an unusual 4-4-1-1 formation), but when Balotelli came on in the second half and started to stretch their attack a bit more (akin to the 4-3-3 formation we're used to seeing from Milan), they were much improved.
They were far more active attacking the flanks and highlighted that Barcelona's defense tends to isolate their central defenders when put under pressure out wide.
When Balotelli drifted wide, Mascherano followed him, but he simply wasn't good enough (or strong enough) to handle the physical threat of the Italian striker.
He was forced to foul him time and time again, and when he didn't, Balotelli skipped past him with ease—as shown in the image below. It's important to note here that once Balotelli has beaten the wide man, look how isolated Barcelona's defenders are across the back.
There's shape, but it's an isolated shape that can be picked off by central runners. Had Robinho still been on the field at this stage, it could well have been him.
Robinho might have seemed ineffective in the first half, as he was marked out of the game by Pique, but indirectly, he actually had a huge influence on Milan's attack.
As shown below, his run into the middle freed up space out wide. Had Nigel De Jong's pass been better, he would have been able to better expose the isolated full-backs. Both Kaka and Ignazio Abate were in positions here to do just that with their strong runs.
The same happened on Kaka's cross culminating in Pique's own goal.
Kaka broke free down the right flank courtesy of a lovely move on Dani Alves, and suddenly the space was there to be had. Three Barcelona defenders tracked the run of Robinho through the middle, and that allowed Kaka time to collect the ball and run into the box.
Ultimately, that would be enough to put the ball into the back of the net.
As mentioned before, Barcelona's weakness out wide wasn't enough to give Milan the victory here—or even give one of their players a goal—but it was enough to show that La Blaugrana still have work to do in this department. Barcelona have always seemingly had one defensive issue or another in recent times (at centre-back, in the air, out wide) and it's important that Gerardo Martino addresses these problems before they start to become biggers problem in either La Liga or the Champions League.
Barcelona are rarely going to have problems scoring goals, but they are going to struggle to make a serious dent on the competition if they can't stop goals.
Which, with a bit of luck for Milan, could have been a real problem this week.
It was better, but a long way from perfect, for Barcelona.