The attitude of the players was thought to be poor under Andre Villas-Boas, who consequently lost his job with Di Matteo taking over as caretaker manager at the beginning of March.
Di Matteo has since turned the Londoners' fortunes around and they now find themselves in the FA Cup final and have a semi-final lead going into the second leg against Barcelona in the Champions League.
"It has been pretty intense from day one because, apart from one week, we've played every three or four days," said Di Matteo.
"But that's the price of success when you manage to reach the final of the FA Cup and the semifinal of the Champions League so we're very pleased to be challenging ourselves in these competitions.
"It's important the players know the responsibility they have to the club and the supporters, and to the players themselves. A footballer's career is very short and every season you have a chance to achieve something and every year you have to try your best to do that. You don't know when there is going to be another chance for you."
Chelsea are preparing to face Barcelona on Tuesday following their goalless draw at Arsenal on Saturday.