The breakthrough arrived in just the 10th minute. Ntsabeleng finished calmly from the left side of the box after a precise through ball from Marcelo Allende, giving Sundowns an early advantage they would not relinquish.
Sundowns dominated the early stages and came close to extending their lead. Arthur Sales struck the post in the 18th minute after being set up by Aubrey Modiba, before forcing a close-range save from Darren Keet earlier in the move.
Durban City responded with occasional counter-attacks, but Bokang Mokwena missed a good chance on 33 minutes, firing narrowly wide after a quick break.
The visitors continued to threaten before the break, with Modiba and Ntsabeleng both missing from distance, while Keet remained alert to deny further efforts. Durban City nearly found a leveller in first-half stoppage time, but Mokwena again missed the target from inside the box.
After the interval, Sundowns pushed to kill the game. Brayan Leon hit the post in the 50th minute following a cross from Jayden Adams, while Tashreeq Matthews and Leon both missed further opportunities as the pressure mounted.
Durban City showed improved intent in the second half, winning several set-pieces and corners. Fezile Gcaba headed over from a tight angle, while Samkelo Maseko's introduction added urgency in attack. However, their efforts were disrupted by a series of fouls and bookings, with Gcaba, Maseko, Brooklyn Poggenpoel and Kyle Jurgens all cautioned.
Sundowns managed the closing stages professionally, introducing fresh legs including Themba Zwane and Iqraam Rayners. Rayners had a late chance but fired wide, while Zwane won a crucial free-kick deep in stoppage time to ease the pressure.
This victory allowed Sundowns to cement their position at the top of the Betway Premiership table. They had started the match on 53 points, just ahead of Orlando Pirates, and the three points lifted them to 56, widening the gap at the summit.
Durban City, who had been sixth with 35 points before kick-off, remained on 35 points after defeat and now risk slipping further down the top eight as other teams completed their fixtures.