Olum was all alone in the middle of penalty box when he booted home his first goal in 41 career games for Kansas City (17-10-8), which at 59 points ended the day in sole possession of the best record in the MLS.
The New York Red Bulls, who have 56 points, have one game remaining Sunday against Chicago.
Olum also recorded his first career assist on Graham Zusi's tally in the 47th minute.
Jack McInerney scored for the Union (12-12-11).
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