De Zerbi said: "I think we played a very good second half and the second part of the first half as well. We know the qualities of Chelsea.
"I think we gave our best and we have another game to reach the top 10 position.
"It has been a very tough season and the fans have understood everything.
"We have competed in a good way but have lost too many points at home, especially in the first part of the season and we have paid for that.
"I think it was a clear penalty today. But the problem is not VAR, the problem is the level of the referees. Today I did not like the performance of the referee.
"But I make more mistakes than the referee.
"I am happy for this season but I am sorry because I am disappointed and wished we would compete in a different way. Next season we can be a stronger squad and team."