I think the best way to beat Chelsea is to exploit the space behind their wingbacks. We need players to occupy the wings and Dembele would be ideal for that because 1. He would provide more options in the attack and create more space for Messi and Suarez and 2. He would keep Marcos Alonso quiet and the latter can't go forward and support the attack as he often likes to do and Hazard would probably get instructions to support him in defense because Messi spend's a lot of time on the right side too. So although Dembele doesn't do much defensive work he can help Roberto indirectly by keeping the danger away from his side and at the same time Roberto will not have to do a lot of work in the attack and can stay back and this will help avoiding counter attacks and save a lot of his energy, as we know he tends to get exhausted early with all the work he does. A lot of Chelsea's attacking play comes from their wingbacks so if you can stop them from going forward you are doing a great defensive work and at the same time you have more players on the field who can score or create goals.
Option1:
MATS
Roberto Pique Umtiti Alba
Rakitic Busquets Iniesta
Dembele Messi Suarez
Option2:
If Dembele doesn't start then we need Messi to play more on the wing because that's where he can find more space ,because as you would imagine Conte will try to crowd the midfield area where Messi is expected to play. It will be the same 4-4-2 formation but with Alba as LMF and Digne as RB. Alba as we know is great in supporting the attack and recently even scoring some goals and at the same time he is a defender and would provide a lot of support to Digne. So without doing much of physical defensive work Messi and Alba on the wings would stop a big part of Chelsea's attacking play which is created by their wingbacks. In this case we also don't have any of Gomes, Paulinho or Vidal on the field. Digne isn't a great LB but what he has been lacking there the most is the attacking work which he will not need to do much of in this line-up.
MATS
Roberto Pique Umtiti Digne
Rakitic Busquets Iniesta Alba
Messi Suarez
Avery important thing this two options provide is the element of surprise which can be very helpful in unlocking Conte's parked Bus. In a game like this you need some unpredictability because Conte and his team surely have been analyzing Barca since the draw and to surprise them like this would interfere with their prepared tactics.
