The Brazilians' supporters brought the club into disrepute at the Lucas Moripe Stadium, and Downs sent out an apology afterwards condemning their fans' behaviour. The fans threw objects at officials during the 1-1 draw.
Sundowns stated in their apology on the club's website: "We wish to unreservedly apologise to the PSL, its sponsors, and to the supporters of football in our country.
"The Club views this matter in a serious light and we have launched an investigation into the incident to try and identify the spectators involved so that we can take appropriate action."
The fine is suspended for 12 months, and the club must make announcements asking fans to behave properly before all future matches kick off, as well as at half time.