Zimbabwean striker Evans Rusike netted in the 12th minute for bottom-placed United, who picked up a point in their previous nine games.
The Team of Choice are now a point behind AmaTuks, who extended their winless run to seven matches in all competitions.
Tuks threatened early on, as Thabo Mnyamane poked an effort wide after being set up by strike partner Lennox Bacela in the seventh minute.
However, Maritzburg went ahead soon after, as Rusike beat Washington Arubi with a long-range strike at Tuks Stadium.
The hosts pressed before the break, with Atusaye Nyondo and Partson Jaure having chances but without reward.
Arubi was tested early into the second period as he pulled off a fine finger-tip save to steer an effort onto the crossbar.
At the other end, Maritzburg goalkeeper Tawfeeq Salie had to be alert to foil Jaure at his near post in the 75th minute.
Salie impressed again late on to save a free-kick from Mnyamane and help his side to a morale-boosting result.