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The first legs of Champions League semifinals provided a pair of outstanding matches. With a total of six goals scored and chances estimated around seven or eight expected goals, these were open, attacking contests. Juventus beat Real Madrid, 2-1, to set up a showdown at the Bernabeu in the return leg. Barcelona dominated Bayern Munich, 3-0, and made its return leg nearly academic. What made the difference?

For Juventus, the key was attacking a Real Madrid weakness. With superstar playmaker Luka Modric injured and defensive midfielder Asier Illaramendi out of favor, Madrid Manager Carlo Ancelotti shuffled his lineup. He played defender Sergio Ramos on the right of a midfield two, paired with Toni Kroos on the left. This pairing had been effective in the quarterfinal against Atletico Madrid, but Juventus seemed to have it sniffed out early.

Kroos was charged with driving forward from midfield while Ramos held the line in front of defense. On the flanks there was a similar pattern. Marcelo attacked from his left fullback position while Dani Carvajal remained mostly in reserve. The effect was a lopsided defense, and Juventus pounced on it from the start. Of Juve’s completed passes into the attacking third, about half were played down Madrid’s weaker left flank, compared to passes down the center of the pitch or on the right flank.

When Juventus looked to pass into the box, in was in the channel between the fullback and the center back on that left side. The Italian side completed five passes into the box on the left, and only one on the right. The opening goal by Alvaro Morata was created when Carlos Tevez found space in that channel to receive a pass and get a shot away. It was saved but Morata cleaned up the finish.

Madrid had good chances and certainly could have equalized. But now heading into the second leg, if Modric is not fit, Ancelotti will need a midfield solution that does not imbalance his squad and allow Juventus to pick out chances.

There are fewer decisions to be made by Barcelona or Bayern Munich after a 3-0 first leg. The chances of Bayern going through to the final are now in the single digits. And worse, the only way for Bayern Munich to recover is to get numbers forward and take risks in order to get those goals back. As Barcelona proved on Wednesday, taking attacks risks against the likely Spanish champions is a terrible strategy. The Barcelona counterattack is the most dangerous weapon in world football, and those attacking risks allowed Lionel Messi, Luis Suarez and Neymar space in the open field to create.

This season in La Liga Barcelona has an unimpressive total of 39 shots created from fast attacking moves of over five yards per second. Most clubs have over 40 shots from fast attacks, and Rayo Vallecano has attempted 75. However, Rayo has scored only four goals from shots off fast attacks, while Barcelona has scored an incredible 19. In general, opposition teams sit too deep and play too conservatively against Barcelona for Messi, Suarez and Neymar to have room to counter. But when space opens up, they are freakishly deadly.

This graph shows how Barcelona dominated the first 15 minutes of the match and then the final 15 minutes of the match, but were kept mostly in check in between. It was in those terrible 30 minutes for Bayern that the German side was attempting to attack, enabling Barcelona to counter.

First, Bayern Manager Pep Guardiola opened the match in a shocking man-marking system, apparently hoping to create turnovers from the press but functionally leaving Barcelona’s front line each in single coverage. Barcelona created several big chances early but Manuel Neuer stood strong in goal to keep the match level until Guardiola switched to a more conservative back four.

After the failure of that first risky move, it seemed Bayern might settle into the match. From the 15th minute until the 75th, Barcelona created chances worth only about 0.9 expected goals, slightly less than the expected goals value of its chances from just the first 15 minutes. Then Messi happened. With one perfect strike from outside the box, he gave Barcelona the lead. Bayern tried to respond, but once again risk-taking against Barcelona backfired. Bayern was unable to create any chances of note while Barcelona scored twice and created several attacking chances at speed.

It is extremely hard to see Bayern recovering from this defeat because we have already seen how Barcelona can punish any team that takes risks. Any strategy to win the tie will necessarily open up counterattacking chances for Barcelona.