The Brazilian had a strained relationship with the previous trainer, but he believes the side played without any shackles in the 4-1 win over Dusseldorf
The 59-year-old was fired by die Wolfe last week after the club sank to the bottom of the Bundesliga table and scored only two goals in the opening eight matches of the season, while his working relationship with the Brazilian deteriorated at the end of the 2010-11 campaign.
Attacking midfielder Diego was loaned out to Atletico Madrid last term and returned to the Volkswagen-Arena at Magath's request, but in the team's first match since the outspoken trainer's departure, they triumphed 4-1 at Dusseldorf with the 34-cap international assisting Ivica Olic and scoring a penalty.
"It was really great fun," Diego told Bild. "We enjoyed the 90 minutes. I hope our old coach can be happy, like we are now.
"All the players were free, it was unbelievable. No-one was afraid of making mistakes. [Interim coach] Mr Lorenz [Kostner] prepares each player intelligently and with respect."