From 8th to 2nd, what is so special about this formation? 5 wins, 16 goals, 0 conceded straight from a 3-0 defeat to now a 4th placed Arsenal. What exactly, has changed? 

He introduced the 3-4-3, with 3 CB's guarding the goal. Cesar on the RCB, Cahill as LCB and Luiz in the middle. Now we have seen other managers use the 3 CB's formations before (LvG's United), but there's more to this than just a formation but first let us look at the defense. Luiz, who was formerly known as a more dynamic, ball playing defender now stays back and has the least touches on the ball among the defenders. As a result, he now has made 0 mistakes with the highest tackles per game, blocks per games, and clearances per game among the Chelsea defenders. Working almost like a sweeper he has been very effective and efficient. Revival of Gary Cahill and the forever dependable Cesar Azpilicueta also makes this defense very hard to break.  

The 3 CB's have two wingbacks who make the defense a 5-man defense when staying back. I don't think anyone foresaw Victor Moses actually having a career at Chelsea. After being on loan for 3 years, he now has found himself as one of the key players of the team. Along with Alonso, Moses adds security to the defense and adds the valuable width in attack. Constantly hugging the touchline, these wingbacks have been something Chelsea lacked since the days of Ashley Cole.

On top of this, the CM pairing also sits in to fill in the gaps, choking out the oppositions' attack. This overall adds up to at least 7 players, guarding all the gaps the opponent can try and exploit. The whole team works as a unit due to their given roles complimenting each other. Kante and Matic for example are not deployed as defensive central midfielder at all times. In attack, we have seen either or both add the extra bodies to make sure the strikers can push forward or break through the defense. Matic now has 5 assists due to this change of role, only second to Kevin De Bruyne. After over a season and half full of disappointing performances, Matic finally seems to be getting back to his best in his current role.

Now the front 3, they have among themselves 18 goals and 9 assists. The combination of Eden Hazard and Diego Costa has always been one to worry about for the defense but in this new shape, Eden has been given the freedom to play off Costa. As a result, he now has 5 goals in the last appearance and an assist, while Costa is the league top scorer with 9 goals and 3 assists. Not to forget, Pedro now is tied second in the league with Matic at 5 assists as well. All these numbers are due to their freedom in not having to run back to defend all the time. Teams need to put more bodies in attack to try and break Chelsea's defense and as a result, when they lose the ball they are more susceptible to counter attacks. Exactly how Chelsea have been scoring most of their goals. A swagger about their game, and stealth in defense has changed how people were looking at Chelsea at the start of the season. Will this be enough to take them to the top come May? We will just have to wait and see how they manage to go through the next couple of months as the fixtures pile up and players get tired.