Pablo Mastroeni scored the other goal for Colorado (8-6-6) and Omar Cummings had three assists as the Rapids avenged a 2-1 loss to Chivas on March 21 and improved to 6-2-3 at home.
Casey had his second three-goal game of the season and third of his career in his first match back after missing the previous two because of yellow-card accumulation and a left thigh injury.
The loss was the fifth straight for Chivas (8-7-3), which has one goal during the skid. The team has been shut out three consecutive times.
Chivas played without goalkeeper Zach Thornton, out because of a strained right quadriceps. Replacement Lance Parker made his MLS debut.
The Rapids wasted little time building a 2-0 lead. Mastroeni scored his first goal of the year 26 seconds into the match and Casey sent a shot over Parker's left shoulder in the fourth minute.
Later, defender Shavar Thomas received a red card ejection to further deplete Chivas' ranks.