Chiefs made heavy weather of beating a defensive Sundowns at a jam-packed Super Stadium to reach the semifinals.
On the run of play Chiefs could easily have embarrassed Downs by a much bigger winning margin.
The only goal was scored by Mandla Masango in the 83rd minute.
Chiefs missed countless chances and could have won 6-0 had they take their chances.
Downs were a huge disappointment to their fans in the capacity 28 000-strong crowd, and failed to force Arthur Bartman into a save.
At the other end, the Brazilians' veteran keeper Brain Baloyi was one of the busiest players on the pitch.
Downs also had Mabhuti Khenyeza sent off in the dying minutes by referee Buyile Gqubule for a second bookable offence.
Amakhosi wasted a number of chances against a hesitant Downs side and when they did manage to find the back of the net in the 42nd minute George Lebese's header was ruled offside.
Downs caretaker coach Trott Moloto opted for a conservative approach using a lone striker in Khenyeza who was ineffective, but received little support from midfield.
Chiefs had a shout for a penalty denied in the third minute when Elias Pelembe appeared to pull down Knowledge Musona inside his penalty area.
But referee Gqubule waved play on.
Baloyi had a busy first half. He did well to turn Abia Nale's dangerous shot for a corner in the 11th minute and stopped a close range shot from Musona, before fisting away a goal-bound free-kick from Mandla Masango.
But the miss of the match went to Lebese in the 28th minute when, after rounding Baloyi, he hesitated and allowed the keeper to recover and clear the danger.
Masondo fired another shot over the crossbar in the 36th minute and then came Lebese's disallowed goal three minutes from the break.
While Chiefs were on top they failed to capitalise because of their powder-puff attack and weakness at free kicks.
Downs defender Luvhengo Mungomeni came to Baloyi and his team's rescue in the 52nd minute when he did well to boot Musonda's shot off his goal-line as Amakhosi kept up the pressure.
Masango finally got it right when he latched onto a Nale through-ball and slotted home seven minutes from time much to the relief of the Chiefs fans in the capacity crowd.
But more disaster struck Downs when Khenyeza, who struggled all afternoon against the well-marshalled Chiefs defence, got his marching orders in the 90th minute for a second bookable offence.