Goals from Bradley Grobler (two), Jeremy Brockie and Kingston Nkhatha sealed the victory for SuperSport, who also missed a penalty in the game.
Pirates grabbed a consolation when Oupa Manyisa scored a spot-kick deep into injury-time, but it was another desperately disappointing night for the side.
SuperSport now retain the title they won against the same opposition last season and will play again in the African Confederation Cup in 2018.
SuperSport made the brighter start and had the ball in the back of the net inside two minutes, but Grobler's effort was correctly ruled out by referee Phelelani Ndaba for offside.
Morgan Gould then saw his header drift wide from Thabo Mnyamane's free-kick, while Grobler flicked a cross wide at the near post as Abbubaker Mobara did just enough to put him off.
It took until the 32nd minutes for the first clear-cut chance on goal and it was converted by Grobler.
Pirates failed to clear their lines and Reneilwe Letsholonyane fed Grant Kekana on the right. The fullback turned inside and crossed with his left, leaving Grobler to tap home.
Pirates' first real opportunity came after 39 minutes when Dove Wome, who is on loan at the club from SuperSport, got on the end of a pass, but United goalkeeper Ronwen Williams made a good point-blank save.
SuperSport had an excellent chance to double their advantage on 54 minutes when Happy Jele was adjudged to have brought down Thuso Phala.
There was contact between the pair, but it was minimal and perhaps justice was done when Siyabonga Mpontshane dived to his left to save Brockie's spot-kick.
Brockie made up for that miss minutes later when he put SuperSport 2-0 up with a header from Grobler's cross from the left. Jele might have done better in cutting out the ball.
And it was 3-0 three minutes later with more poor Pirates defending. Phala did well to get into a crossing position on the right, and his ball was deflected into the path of Grobler, who supplied the finish.
SuperSport continued to pile on the pressure and Grobler, Phala and Brockie missed chances, before Mnyamane hashed a sitter wide.
But it was 4-0 minutes later as Nkhatha, who had only just come onto the field, lashed the ball home after a fine dummy from Letsholonyane.
Manyisa grabbed a consolation for Pirates whne he netted a penalty after Maphosa Modiba fouled Luvuyo Memela in the second minute of injury-time.