Both the first legs of the Champion League semifinals were won by one-goal margins by the home team. This doesn't sound like the most thrilling news -- one-goal home wins in continental competition are pretty common -- and yet so hooked had the world become on the notion of a Real Madrid - Barcelona final that it has shaken the European game.

Could it be that the domination of the big two in Spain is not quite so great as everybody had thought? Could it be that those monstrous tallies of goals both sides are racking up in La Liga are illusory? Could we end up, somehow, with the final nobody expected, Bayern Munich against Chelsea ?

BARCELONA (0) v CHELSEA (1)

Had it just been one game, there'd be little reason to worry. Barcelona wasn't at its fluent best, partly because of Chelsea's tactical set-up but also because of its own failings. For three games in a row -- against Levante, Chelsea and Real Madrid -- it has struggled against an opponent which sat deep and packed the center. The actuality of the signing of Zlatan Ibrahimovic didn't work out, but the logic of it becomes clearer by the day: at the moment, with such a lack of height in the side (Sergio Busquets was the only outfielder over six-feet tall in the first leg), a team can let Barca cross, knowing the probability is on it winning the header.

During the game Real had Khedira and Xabi Alonso sitting deep; Chelsea had Frank Lampard and Raul Meireles flanking Mikel John Obi, who possibly had the finest game of his Chelsea career last Wednesday, not merely shielding John Terry and Gary Cahill, but pushing out when required to make tackles and interceptions and to pressure Barca's midfield when it had the ball in and around the center-circle. A packed center means less space for Messi and also makes it harder for midfielders such as Cesc Fabregas, Andres Iniesta and Xavi to break forward. That is a particular problem for Barca with David Villa out with a broken leg and Pedro yet to find his form after injury; both are adept at starting wide -- and so keeping opposing defences stretched -- but then cutting in to offer passing options and goal threat.

Messi, against both Chelsea and Barca, looked more dangerous when he got the ball deep and was able to run at defenders, but to do that he needs players beyond him. Although he has excelled in the false nine role -- he has defined it in many ways -- it may be that, for this game at least, he needs another attacking presence ahead of him, which could mean Alexis Sanchez, fitness permitting, playing as a central striker as he did for much of El Clasico at the Bernabeu. Given his natural drift is right, Barca could effectively play without a right-sided forward, using Dani Alves to get forward down that flank, although that probably requires the return of Gerard Pique to play as the right-sided center-back in what would effectively be a back three. In turn, unless Iniesta is used on the left, that probably means Fabregas will miss out.

There's little reason for Chelsea to change system. Ashley Cole and Ramires were superb in neutering Dani Alves -- disrupting that partnership is another reason to pull Sanchez central -- and the only real decision for Roberto Di Matteo to make is whether to play Didier Drogba or Fernando Torres as the main striker. Drogba's aerial ability clearly unsettled Barca, but equally it can be vulnerable on the break -- as Cristiano Ronaldo proved -- which is where Torres could come in. And if Chelsea could nick a goal, of course, it would leave Barca needing three, effectively giving Chelsea two additional lives.

REAL MADRID (1) v BAYERN MUNICH (2)

Tactically, the key to the game is the Real left, the Bayern right, where Cristiano Ronaldo meets Arjen Robben. Or rather doesn't meet, because neither do much in the way of tracking their full-back, both preferring to stay high up the pitch and focus their energies on attacking. In the vast majority of games, that reluctance to track doesn't matter because Bayern and Real are dominant enough that the opposing full-back will barely dare to venture forward. In the highest-level games, though, it can make both wingers -- while potential match-winners -- a liability.

Fabio Coentrao, the Real Madrid left-back, had a dire game last Tuesday but it wasn't entirely his fault. Again and again he was left isolated against Robben (or Franck Ribery on the occasions when Bayern's wide men switched flanks) and at times he was left facing both a winger cutting in and Phillip Lahm, the Bayern right-back, overlapping. In part the issue was structural, but it only became an issue because Bayern were able to dominate the middle. Had Real had the edge in central areas it could easily have been Lahm left isolated against Ronaldo with Coentrao overlapping -- as it may be on Wednesday.

So how were Bayern able to dominate the center? Essentially it was all down to the alignment of their 4-2-3-1 as opposed to the central triangle in Real's ostensibly similar formation. A week earlier, in effectively surrendering the Bundesliga title by being beaten 1-0 at Borussia Dortmund, Bayern had set up with Luiz Gustavo and Toni Kroos deep in midfield with Thomas Muller as the central attacking midfielder. With Dortmund pressing high up the pitch, the effect had been to break the team, so Bayern ended up with too much space between its back six and the front four, at least until Bastian Schweinsteiger was brought on for Muller, with Kroos pushing up into his position. Suddenly the balance looked better and the connection between front and back was restored.

The Luiz Gustavo-Schweinsteiger-Kroos triangle that Bayern began against Real broke the Spaniards. Mesut Ozil and Cristiano Ronaldo -- as well as the center-forward, Karim Benzema - were all left high up the field. Angel Di Maria did track back and it was noticeable that the Bayern full-back on that side, David Alaba, only started to push forward late on when Ronaldo shifted across to that flank, but with Sami Khedira and Xavi Alonso both forced deep, Bayern were able to advance -- despite Schweinsteiger having an indifferent match -- and play the game largely in Real's half.

The troubling aspect for Real is how fatigued it looked, Xabi Alonso in particular. Admittedly Barca looked rather more tired -- both against Chelsea and then in El Clasico -- but Bayern looked the fresher side, which perhaps gives the lie to the claim that the Spanish league is Real, Barca and 18 sacrificial lambs. What Jose Mourinho must do is work out a way of winning the battle in the center -- which may mean going 4-3-3 and leaving out Ozil for an additional central midfielder.