Apart from a general tightening-up of the midfield and the defence, the most interesting change between Jose Mourinho's Chelsea and previous editions is the emergence of a real plan B. In previous years, managers would make minor tweaks to their preferred systems in order to chase a game. This time, in the three league games in which Chelsea have been facing unfavourable results late*, the Blues have switched to a three-man back line in order to recover the points. The switch has worked, too -- although it failed to prevent the 1-0 loss at Everton, it's been responsible for turning a pair of 1-1 draws into victories in the club's last two matches.

*Draws at White Hart Lane and Old Trafford are obviously perfectly fine.

The question as to why we were confronted with the spectre of 1-1 draws against Norwich then Cardiff City will have to wait for another time (Chelsea still haven't really worked out how to break down defensively-orientated sides, nor has their defensive work been good enough to shut even inferior opposition down). What I'm interested in right now is how and why the 3-5-2 is working.

Note: 3-5-2 is probably a misrepresentation of what exactly has been going on. The game at Carrow Road, for example, only featured a single striker even after the change to the three-man back line. But we'll stick with the above nomenclature for simplicity's sake.

Here are the substitutions that have triggered Chelsea's shape changing in the three matches in which the 3-5-2 has been deployed:

In the Everton game, the switch to 3-5-2 was Chelsea's last substitution of the match, with Mourinho's first move a double swap, introducing Oscar and Frank Lampard for Juan Mata and Andre Schurrle. But more recently, the manager's been more aggressive with the change.

Branislav Ivanovic is the man who allows this all to happen. His ability to play both centre back and right back (and it's not unreasonable to suggest that his ideal position might be as something in between) means that Chelsea can switch from a four-man back line to a three by withdrawing the left back from an attacking player, which is what Mourinho's done each time he's moved to 3-5-2. It's not clear whether Ivanovic is favoured over Cesar Azpilicueta because he allows for this tactical variation or if Mourinho's developed it because he favours ivanovic at right back, but either way this revolves around the Serbian.

The defence is obviously well-suited to a 3-5-2. Elsewhere it gets a little complicated. We've seen all of Eden Hazard, Willian, Ramires and Andre Schurrle as wing-backs, and it hasn't always worked. At Goodison Park in particular, Hazard was an absolute mess playing on the left, leaving the defence horrendously exposed to the counterattack.

The central midfield has also been a little bit odd in this new shape. It's not a Juventus-style system, which is based around a highly structured midfield -- Chelsea don't really have access to one anyway. Instead, it's entirely chaotic. At one point during the Norwich game, we saw a midfield triangle of Frank Lampard, Oscar and Juan Mata, which has the defensive solidarity of a wet paper bag. The double pivot of Ramires and Lampard was preserved during the Cardiff game, but without a very sturdy midfield core, the 3-5-2 means Chelsea are very, very open at the back.

Which, of course, is precisely the point. The formation change isn't really a tactical one -- rather, it's a transition from tactical order to a complete and utter mess. With Chelsea looking open, the other team is baited into trying to exploit that, losing their own shape in the process, and thanks to the quality of players at Mourinho's disposal, placing them in a chaotic situation means that they'll be able to take advantage more easily than their opposition.

It's a very high-risk strategy, as we've seen every time it's used. The Blues looks extremely vulnerable when they don't run four at the back. But when the balance is tilted in favour of Chelsea scoring the next goal and the risk involves dropping a point while the reward means gaining two there's not a real argument that it's not worth employing.

I don't think I've ever seen a plan B that revolves around destabilising the whole game before. The 3-5-2 won't always work, but that it's being employed with some success right now is fascinating.