Sebastien Le Toux opened the scoring in the 17th minute for the Union (0-1-0), but SKC (1-0-0) then reeled off the next three goals to take control of the contest.
Zusi scored the equalizer in the 41st, then assisted on Orior Rosell's game-winning tally in the second half.
Claudio Bieler added an insurance tally on helpers from Zusi and Chance Myers in the 83rd.
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