Sundowns on Sunday recorded a 1-0 victory at Stars, who are the only team still without a win this season as they prop up the Premiership standings with two points from seven games.
De Sa took charge of Dikwena in September - amid talk of a possible sale of the club - following the sacking of Englishman Peter Butler barely two matches into the campaign.
The side was also rocked last week by the resignation of general manager Senzo Mazingisa, and Mosimane insists De Sa is doing well in Rustenburg given the circumstances.
“Roger has done well here,” said the Gauteng Sports Awards' Coach of the Year.
“You might be looking at the result and say how many games have they played, how many have they not won. It's not about that.
“He found a team in a difficult position and he is trying to stabilise the team, and to be honest he doesn’t have as strong personnel as us. We are a little bit lucky.
“I feel for him as a brother and coach, and he has done well.”