In a game delayed more than an hour in the first half by a thunderstorm, the Rapids scored the equalizer when Chris Klute found Castrillon with a crossing pass and the Colombian midfielder headed it into the net.
Deshorn Brown scored in the 9th minute for the second-place Rapids (9-7-8), who won the Rocky Mountain Cup for the first time since 2006.
Colorado stretched its unbeaten streak to seven games and remained one point behind conference-leading Salt Lake with the result.
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