Thabiso Nkoana, Kermit Erasmus and Sibusiso Zuma all found the back of the net.
Matsatsantsa will clash with Mamelodi Sundowns, who beat Free State Stars yesterday.
United coach Gavin Hunt made seven changes to the side that played against Orlando Pirates in their last match.
AmaZulu started brightly, with Siyabonga Vilane hitting the crossbar, and Marc van Heerden shooting just wide. Goodman Dlamini had his chance saved by Ronwen Williams, after an error by Davis Nkausu.
In the 33rd minute AmaZulu had another chance as the United defence failed to clear properly and allowed Vilane to nip in, but his shot was straight at Williams who got in a strong block.
Usuthu were made to rue those missed chances when Matsatsantsa went ahead on 35 minutes. Erasmus ran up the wing and crossed to Nkoana, who simply had to nudge the ball home, and the match went into half-time 1-0.
After the break Van Heerden took a free-kick in a promising position, but he did not get enough power behind the shot and Williams had an easy save.
Substitute Zuma nearly made it 2-0 soon after coming on, but shot wide. Nkoana then had a one-on-one chance with Tapuwa Kapini, but the keeper won the battle and made the save.
However, with a quarter of an hour to go, SuperSport's enterprising game paid off whe Erasmus hit home the rebound from Nkoana's shot.
SuperSport put the result beyond doubt at the death, when the ball was floated into the AmaZulu area where Tsweu Mokoro completely misjudged the flight, and Zuma showed good skill to flick the ball up and over the second marker.
Although the SuperSport man looked to have wasted the chance, he turned quickly and fired his shot which ricocheted off the defender and goalkeeper before hitting the back of the net.