Rudolph Bester was the hero for the home side, scoring a brace, after Gert Schalwyk had opened the scoring in the fifth minute.
The result severely dents second-placed Ajax's title hopes.
Kurt Lentjies whipped in a corner and found Schalkwyk 12 yards from goal. The United player made no mistake with a clinical finish to give his side the lead, 1-0.
The home side continued to press forward and Lentjies should have found the game’s second goal when he rose to meet a Diyo Sibisi cross, but his header from six-yards out was superbly saved by Hans Vonk.
In the 36th minute, Bester let rip with a pile-driver from 20 yards out that beat the keeper, but struck the crossbar much to the disappointment of the home fans.
Maritzburg continued where they left off in the second half, and only had to wait five minutes before they doubled their lead courtesy of a Bester penalty, after Lizo Mjempu was adjudged to have handled the ball inside the box.
17 minutes later and Bester put the result beyond doubt when he grabbed his second of the night, a superb finish saw him lob the Ajax goalie from 20 yards out and seal his side’s victory.