Spurs progressed into the fourth round of the FA Cup with a 1-0 victory over Barnsley at Wembley on Tuesday night, with Alli scoring the winner.
Pochettino said: "For me, Dele Alli is a top player. He is a key player for us. I think he helps us by scoring today. I am so happy with him.
"It's true that everyone can do better but I am happy. It is a period that he needs to find his balance but I am so happy, his performance was good. He tried and scored and that is fantastic."