Barcelona put one foot in the quarterfinals courtesy of a 2-0 victory over Manchester City at the Etihad Stadium on Tuesday night.
Lionel Messi and Dani Alves scored the goals in an entertaining, tight tactical battle, but the result will be shrouded in controversy given the decisions made by the referee.
Let's take a tactical look at how the game played out.
Manchester City dispensed with their usual free-flowing 4-4-2 formation and instead switched to a rigid 4-4-1-1. David Silva played as a No. 10 behind Alvaro Negredo, and Aleksandar was brought in to play left midfield ahead of Gael Clichy.
Barcelona rocked up with their usual 4-3-3, but it was as lopsided as can be with Cesc Fabregas roaming off the left flank. He would pop up anywhere from next to Dani Alves at right-back to playing on the shoulder as a No. 9.
City set their stall out
In the first 10 minutes of the 2009 UEFA Champions League final, Barcelona rode out 10 minutes of relentless pressure from Manchester United before growing into the game and beating them 2-0.
This time, Manchester's other club had to sit back while Barca asked the questions, and it was here that Manuel Pellegrini's stout 4-4-1-1 revealed its defensive colours.
Yaya Toure and Fernandinho were trusted to hold the fort in a two-man midfield, throwing their physical, yet mobile, bodies around to put off playmakers Xavi and Andres Iniesta.
Kolarov was brought in as a flat LM to shield Clichy from the incisive runs of Alexis Sanchez and Dani Alves, and the Serbian's presence—while not ground-breaking—stemmed the flow of switch-balls from Xavi to Alves to an extent.
With Sergio Busquets so deep in possession (keeping an eye on that pesky David Silva), it was essentially one vs. one across the board with City the physically superior team. Barca had plenty of the ball, but Yaya Toure, Fernandinho and Martin Demichelis handled the space brilliantly.
Cesc drifted around to find holes from the left, but too often entered the areas Lionel Messi should have been and Barca looked stunted as a result.
They seemed most potent down the right, but City did a good job pulling numbers back and overwhelming that side of the pitch. With no genuine outlet on the left (Jordi Alba played a reserved game), the visitors had no switch-ball outlet to play.
City grow into it
It took 10 minutes, but City finally got their foot on the ball and started playing.
Much of that was to do with passing angles, as while Martin Demichelis was stepping in and intercepting with regularity, Kolarov, Jesus Navas and Silva were struggling to separate from markers and sprint into space.
Once the outlets got their act together things improved, and City started working the ball to Vincent Kompany to try long, vertical passes á la Mats Hummels of Borussia Dortmund. The aggressive passing worked, and it was the source of the home side's first major chance.
Kompany beat the four-man press from Barca with a single pass, and David Silva rolled Busquets in acres of space to slide Negredo in between the centre-backs.
It highlighted the vast swathes of space in and around Busquets, and City ended the first half in a strong position after working out how to pick on the visitors: beat one line of pressing and you've got Silva one vs. one with the defensive midfielder.
City started the second half in control but one mistake in midfield changed the game, with Lionel Messi steaming through on goal and Demichelis stupidly lunging in on him.
The referee awarded a penalty—the challenge started outside the box but ventured inside—but his red card, as the last man, was justified.
The Argentine stepped up to convert the penalty, and up until that point the visitors had only crafted one chance that looked remotely incisive: Cesc being slipped in on the counter three minutes before, only to lose sight of the ball and run himself into a hole.
It was a 52-minute example of the worries plaguing Barca coming into the game: They only look sure-fire bets to score when counterattacking in quick transitions.
Pellegrini immediately switched from 4-4-1-1 to 4-4-1, dropping Fernandinho into centre-back until Joleon Lescott could enter the fray. Samir Nasri entered at the expense of Kolarov, with Silva switching to left midfield.
This move essentially freed up the full-backs on both sides. Barca relaxed and Alves stopped tracking Clichy, while the switch-ball to the Brazilian from Xavi was firmly back on with Nasri struggling in his defensive brief.
Alves spurned a great chance to make it 2-0 after Clichy disappointed with a cross in space, then Yaya Toure found Zabaleta roaming on the right and Silva's resulting effort skipped wide of the post.
In their defensive shell, City's midfield four began dropping too deep too often, allowing Xavi the space he wasn't getting in the first half due to the dogged persistance of Toure.
An insane pass from the maestro saw Cesc square it for Gerard Pique for a tap-in, but it was wrongly ruled offside. Alves then sealed what seems to be the tie in its entirety by slotting home superbly after linking with Neymar on the right.
Pellegrini set up a strong system that matched Barcelona territoriality and matched them in midfield, allowing pointless possession in exchange for a clean sheet.
But everything changed when Demichelis went off, and their only method of attack—aggressive passing into Silva one vs. one with Busquets—was removed when the Spaniard switched wide.
They tried to reload and use cross-field passes and full-back overlaps to find new ways through, but Barca were good value for the 2-0 win.
Tactical Man of the Match: Dani Alves