There were South Africans on either side in the game as Luke Le Roux started in midfield, but it was Mofokeng who came out on top.
He netted with a header too, latching onto a deep cross and looping his effort over the goalkeeper from 15 yards to score his side’s fourth.
The Bafana Bafana midfielder was not done, though, as he then laid on the fifth goal for Union as they stayed in third place, two points behind leaders Gent.
The 22-year-old now has five goals and four assists in 14 matches in all competitions this season. It is the first time since he moved to Belgium that he has provided two goal contributions in a single game.
It was another dismal day for Le Roux’s Cercle Brugge, though, as they are bottom of the league without a win from nine games, with three draws and six defeats.
Shandre Campbell’s Kortrijk are second-bottom, with one win and seven defeats in their eight games, but were not in action this weekend.