Ahead of the match Brian Baloyi told KickOff.com that the club would donate R10,000 per goal they scored, in honour of October being breast cancer awareness month.
Nyasha Mushekwi and Katlego Mphela got a brace each, and Richard Henyekane added a fifth, to make up Downs' impressive scoreline.
Khetowakhe Masuku got the only goal for Leopards.
Lidoda Duvha, who conceded four goals in the final half hour of the match, will look back on some missed opportunities early in the second half.
The result sees Sundowns move back to within three points of leaders SuperSport United, while Leopards remain second from bottom, two points ahead of Jomo Cosmos.
The first half was a subdued affair until Downs broke the deadlock three minutes into added time, with Mushekwi chipping the ball over the advancing Posnett Omony after sprinting onto a great through ball.
Leopards had chances to equalise in the early stages of the second half – Mongezi Bobe and Rodney Ramagalela both spurned good chances that originated out on the flanks.
Mushekwi doubled Sundowns' advantage on 63 minutes, beating Simphiwe Vezi to Teko Modise's corner kick and scoring with a good header.
The Zimbabwean was replaced by Mphela soon afterwards, and 'Killer' immediately made it 3-0, cracking home a right footed shot.
Leopards scored a consolation goal on 85 minutes, with Masuku's brilliant direct free kick, but further strikes from Richard Henyekane and Mphela in the 87th and 91st minutes meant his effort was all but forgotten.