Brooks Macek had a goal and an assist for the Hitmen (44-20-5), who extended their win streak to four games, while Jake Virtanen had two assists.
Cody Sylvester scored in his fourth straight game for Calgary and Pavlo Padakin had the other.
Sylvester has five goals and 12 points in his last four games and leads his club with 84 points in 66 contests.
Mathew Dumba had a goal and two assists for the Rebels (39-24-7), who lost for the first time in six outings, and Rhyse Dieno pushed his point streak to four games with two assists.
Tyson Ness and Brady Gaudet each scored once to round out Red Deer's offence.
Chris Driedger made 23 saves for the win as Patrik Bartosak turned away 26 shots in defeat.
Calgary went 2 for 5 on the power play while Red Deer scored two goals on four chances with the man advantage.
Ness had the lone goal of the first period before the Hitmen scored three straight goals in the second period.
Sylvester and Macek scored 37 seconds apart to give Calgary its first lead and Padakin made it 3-1 at 13:01.
Dumba scored for the Rebels late in the second before Gaudet forced overtime with a tying goal at 10:03 of the third period.