Dean Furman's departure at United created an opening for Kudakwashe Mahachi, with Celtic recalling Thato Lingwati and Andile Fikizolo following his impact off the bench against Baroka FC.
Bradley Grobler went inches away from putting United ahead on 18 minutes when his stupendous attempt rattled the crossbar having opened space for the strike.
Siwelele broke the deadlock with their very first attack 14 minutes later after Mzwanele Mahashe propped up unchallenged in the area to turn home a corner-kick with Ronwen Williams off his line.
Matsatsantsa almost pulled level ten minutes to halftime when a cutback in the area from Grobler released Onismor Bhasera, who put Sipho Chaine to work following a low attempt.
Thamsanqa Gabuza was called upon by United as a halftime change in place of Mahachi, whilst Aubrey Modiba applied intense pressure in pursuit of the equaliser.
A coming-together between Modiba and Chaine led to a free-kick near the area and from the resultant set-piece Teboho Mokoena drilled home the equaliser minutes later.
Sipho Mbule looked to pull something out the bag for United on 60 minutes after playing in Grobler, who had Chaine stationed onto his line following a first-time strike.
It was all Matsatsantsa following the closing stages with substitute Ghampani Lungu forcing Chaine to a finger-tip save off a telling delivery seconds from entering.
Both sides looked for the winner late on with their respective goalkeepers Williams and Chaine on their toes, but it finished 1-1 with United staying fourth while Celtic dropped to 11th place.