Jamie Smith had the assist on Casey's goal as the Rapids extended their unbeaten streak to four games (3-0-1). It was Casey's second of the season.
Marco Pappas scored both of Chicago's goals, giving him five on the season. Both were set up by Baggio Husidic.
Pappas' first goal came on a fake off a direct free kick. He curled a 15-yard shot around the Colorado wall, beating goalkeeper Matt Pickens to his right in the 23rd minute.
Pappas gave the Fire a 2-1 lead 46 seconds into first-half stoppage time. The midfielder took Husidic's pass from the right side and drilled a shot by Pickens.
Omar Cummings' 12-yard kick gave the Rapids a 1-0 lead in the 21st minute. His right-footed shot went low and to the right of goalie Andrew Dykstra.
The match was the last for each team for about three weeks. Colorado (6-3-2) comes back from the MLS' World Cup break at Houston on June 26. Chicago (3-3-5) plays at New England on June 27.