Exactly how does Chelsea defeat Barcelona over two legs and advance to the UEFA Champions League final? Nobody quite has that answer, but before diving into the two-legged scenarios, let's just look at the first leg. How are the Blues supposed to get a positive result at Stamford Bridge to just put themselves in a position to possibly pull off the shocker in the second leg?

One way that Chelsea could be successful in the first leg is by exploiting what sometimes becomes a three-man back line for Barcelona. The way their fullbacks get forward, especially Dani Alves, puts the central defense into somewhat of a precarious situation where they have to defense 1v1. According to We Ain't Got Not History's Graham MacAree, with Gerard Pique and Javier Mascherano likely to be the Catalans' central defenders on Wednesday, Barcelona asking those two to defend 1v1 is where Chelsea could take advantage.

You might be familiar with the idea of splitting up the centre backs and dropping the holding midfielder into a back three while on the attack, because it was a favourite tactic of Andre Villas-Boas. It's a useful way of putting the fullbacks into play as legitimate attacking threats, but we should be very familiar with the consequences as well, namely that it puts the onus on individual players not to make mistakes. That's unlikely to happen with Puyol or Sergio Busquets (who is a splendid footballer despite the myriad faults in his character), but Gerard Pique and Javier Mascherano are a different story. Both are good enough, but neither is immune to making trivial errors, and if Chelsea can isolate a player against them and beat them, they'll be in very good shape.

This isn't something that Chelsea can attack all match because it's not a situation that comes up all match, but it will come up sometimes. When it does, the Blues need to take advantage. It is the best way for them to nick a goal or two and throw the tie into flux.

We'll have continuous pre-game updates and live game coverage in our Chelsea vs. Barcelona, UEFA Champions League Semifinals StoryStream. For more on the two teams, head over to Chelsea FC blog We Ain't Got No History and FC Barcelona blog Barca Blaugranes.