If Chelsea can play a defensive game in the match, then I will say thats going to be the worst mistake which they are going to make, if they play a defensive game, then they are going to concede much goals in the match, we already know that PSG is having dangerous attackers, which will find their way to penetrate Chelsea defense if they play a defensive game. If you are playing a defensive game, then they are going to make PSG more comfortable, and they will be more pressure on chelsea which they are going to find it difficult to withstand, so it’s just better Chelsea shouldn’t play a complete defensive game, they should play their normal football.
Playing too defensively will certainly not be beneficial for Chelsea either. They can exploit gaps in PSG's defense, but they must also be supported by players with pace and good finishing.
I think both teams will force each other to fight in midfield. Dominating the match may not guarantee victory, but perhaps each team can try its best to create as many scoring opportunities as possible.