Mondli Cele had given the Team of Choice a first-half lead, but Bongani Ndulula ensured a share of the spoils, despite Usuthu being a man down following a red card shown to Bornwell Mwape.
The first clear chance of the match went the way of the visitors, with Ndulula turning sharply after collecting the ball from a throw-in, only for his shot to flash wide.
Nhlanhla Vilakazi headed over the crossbar soon afterwards before the hosts got the opener on 37 minutes.
Cele switched flanks to the left, received a pass just inside the area and cut inside to beat goalkeeper Siyabonga Mngoma with a low shot just inside the near-post.
Usuthu sent on Ayanda Dlamini at the start of the second half and the change had the desired effect as they started to threaten more, though clear-cut chances were hard to come by.
Mwape almost produced an equaliser on 65 minutes, pushing forward into the box before striking a fearsome left-footed effort across the face of goal and just wide of the far post.
But the striker lost his head soon after – being shown a straight red card for a reckless, studs-up challenge on Ashley Hartog.
However, just a few minutes later the Durban side were awarded a penalty when Ndulula was bundled over in the box by Mohammed Awal. The Bafana Bafana striker took the spot kick himself and emphatically fired it into the back of the net.
United pushed hard to restore their lead, but found Ngoma in fine form. And when the goalkeeper was beaten, Hartog saw his header cannon back off the crossbar.
The result sees Maritzburg move up to fifth, while AmaZulu remain rooted to the foot of the table.