#2 N'Golo Kanté and the defence
In the summer of 2016, Chelsea struck gold by signing N'Golo Kanté for a fee that's trivial in today's market. And he immediately transformed the team by plugging the Essien shaped hole that has been there in Chelsea's midfield for quite some time.
He consistently puts in the tackles and interceptions every single match to make those recoveries and transitions from defence to attack. And he does it with minimum fuss and maximum professionalism, both on and off the pitch.
This allows almost every other player in defence and midfield to play with more freedom as they know that he will be there to plug in the empty spaces. With Kanté patrolling in the middle, the defence conceded just 33 goals in the league last season and got 16 clean sheets.
With a more able partner in Bakayoko this season, Kanté will be crucial once again especially in Europe to help the defenders shut out the attacking teams like Real Madrid, Barcelona, Bayern Munich and PSG.
The man himself will be hungry to prove himself at the European stage for the first time in his career. And for Chelsea to win it all, he will definitely be the most crucial cog.