The South African side dominated proceedings from the start of the match with goal keeper and skipper Ronwen Williams inspiring the team.
The first half ended 2-0 with goals from Tashreeq Matthews in the 11th minute and Peter Shalulile in the 41st minute.
Mamelodi Sundowns continued their dominance from the start of the second half and were rewarded with a third goal in the 60th minute by Miguel Reisinho.
Substitutes, Arthur De Oliveira and Katlego Ntsabeleng came of the bench to score the fourth and fifth goal in the 74th and 84th minutes.
Remo Stars substitute, Samson Olasupo scored the consolation goal from a short outside the 18 yard box in the 76th minute before a large and passionate crowd.
With this result Remo Stars have a huge mountain to climb when they go away for the return leg in Pretoria on Oct. 26.