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The defeat to Chelsea shouldn't be taken as a complete benchmark, PSG will still be considered the favorites for next season Champions League. PSG performance hasn't declined significantly in fact, I believe they're still at their best, just unlucky in the Club World Cup. While it's true that back to back Champions League titles are extremely difficult, it's not impossible.
The form and effort with which Chelsea is playing seems to be able to achieve a lot of progress and one reward for them is that they never bring pride in their players so that their hard work will motivate them to succeed. Only if PSG works hard, they can make their own standards in it, otherwise Chelsea is playing with a good effort. They have lost the match against a team that has been losing for a season and PSG's defense is also quite strong, due to which they should not have lost this match. Their strength is not that good, but they should be given a chance to succeed like before and they should work hard in this too, otherwise their strength is not completely successful. If they achieve this too, it is also no less than anyone because there are quite strong teams playing here too.
You're right, Chelsea was more hardworking than PSG in that finals and that's why they kept getting more chances to score goals than PSG, from the kick off till the final whistle the Midfield was dominated by Chelsea and it helped them to connect with their attackers more, PSG tried to penetrate from the flanks but it didn't produce good results since their attackers were mostly displaced by Chelsea's defenders.
It still suprises me cause PSG has a better squad than Chelsea especially in the Midfield and defence bit suprisenly they suddenly became weak, a team that's defeated Madrid, Bayern Munich, Inter, Atletico etc they need to work on their error else it would affect them in the upcoming Champions league tournament.