Drew Moor and Jeff Larentowicz added first half goals for Colorado (6-6-1). Larentowicz's goal came on a penalty kick for the Rapids, who have won their last two games.
Reserve goalie Greg Sutton batted a shot by Scott Palguta, but the ball came back to Castrillon who put a header into the net.
Defender Tyrone Marshall received a red card ejection in the 59th minute.
Colorado was without forward Conor Casey. Casey was held out with a pulled right hamstring suffered May 19 against Sporting Kansas City.
Patrice Bernier added a goal and Andrew Wenger scored for Montreal Montreal (3-7-3). The Impact are 2-2-2 in their last six games.
Montreal allowed its MLS-leading fifth penalty kick goal.
The Rapids led 2-1 at the half, but missed a chance at grabbing an early lead. Goalkeeper Donovan Ricketts stopped Castrillon from deep inside the scoring zone, but Castrillon got a foot on the ball again and barely missed a second attempt in the fourth minute.
Brenier scored on a give and go from Felipe Martins in the 15th minute. Brenier put the ball on Martins' right foot and Brenier took a blind back pass and found the back of the net.
Colorado tied it at 1 on Larentowicz's penalty kick in the 18th minute. Hassoun Camara held up Wells Thompson deep inside the scoring area that drew the foul and Larentowicz sent a shot past the right leg of Ricketts.
The Rapids took the lead in the 30th minute. Martin Rivero's set up Moor with a free kick from 35 yards out and Moor's avoided the dive of Ricketts in the 30th minute.'
Wenger tied it in the 49th minute. Collen Warner threaded the needle to get Wenger the ball and Wenger avoided Moor to get a shot at an empty net.
Sutton replaced Ricketts in goal in the 66th minute and finished the game.
Wenger missed a quality chance in the 69th minute, sending a shot wide of the left post. Rapids Goalkeeper Matt Pickens went down on all fours to stop a shot by Martins in the 81st minute..