Mosimane's defending champions were on the losing side in a 1-0 defeat as the Brazilians recorded a crucial victory to extend their lead in the group standings.
Striker Peter Shalulile scored the decisive goal in the 23rd minute as Sundowns - moving to 10 points after four matches played - solidified their chances of qualification for the knockout stages.
Speaking after the final whistle, a furious Mosimane lambasted his former side's supporters for obstructing the Al Ahly team bus and forcing it to change route during its passage to FNB Stadium.
"We must talk about what happened at Atteridgeville first when they blocked the bus, Mosimane said.
"When they swore at my mother, my family.
"I don't want to talk a lot about Sundowns. I will tell you what happened even when we played Sundowns last week. There are too many personal things.
"I'm over those things. I don't want to talk about them, it's unbelievable. I don't want to talk anymore. I'll talk about it in my book and my documentary.
"Even now, before every match, they are still after me these people. They don't want to leave me alone. I've moved on. You've got a good team. It's got three coaches.
"I mean really! What do you want? Move on! Leave me, I'm gone. I've done my best. I've given you a great team. Why are you after me, What do you want to achieve?"
Mosimane also insinuated that Sundowns were indulging in the dark arts of the game to influence the result.
"Very dirty. I'll reveal it one day. There's a lot, too much. The game is played on the pitch. The goal is legitimate, no problem. Thapelo's goal in Cairo was a good goal.
"Why do you do other underhand stuff and all that? It's unbelievable. It's really sad to be honest, for such a big team," Mosimane added.