Lebohang Maboe netted an 80th minute decider after substitute Evans Rusike cancelled out Mohammed Anas's first-half opener for the visitors.
The result lifted Maritzburg above Chippa United and Orlando Pirates to eighth on the table with 23 points from 19 matches - five points more than 14th-placed Stars.
Anas drew first blood from inside the area in the 21st minute against his ex-employers.
The Ghanaian, who joined Ea Lla Koto in January after leaving United in the off-season, turned sharply in the box before rifling the ball past goalkeeper Virgil Vries.
However, Zimbabwean forward Rusike equalised in the 65th minute before Maboe struck late for the home side, who drew 1-1 with Polokwane City and lost 2-1 to Kaizer Chiefs and 4-1 to SuperSport United in De Sa's previous games in charge.
The former Ajax Cape Town boss took over the reins from interim coach Fadlu Davids in January, officially succeeding Ernst Middendorp, who resigned in November last year.