Calgary's Jake Virtanen scored on a penalty shot to tie the game 1-1 in the second period and Mack Shields made 35 saves.
The Hitmen lead the series 3-1 and can close it out with a Game 5 win at home on Friday.
Tyler Lewington had a power-play goal in the first period for the Tigers.
Medicine Hat's Marek Langhamer stopped 19 shots.
WHEAT KINGS 3 PATS 2 (OT)
REGINA — Tanner Kaspick scored 3:36 into overtime as Brandon pushed the Pats to the brink of elimination with a Game 4 win in their second-round playoff series.
Peter Quenneville had the tying goal on a power play 7:53 into the third period for the Wheat Kings, and assisted on Nolan Patrick's marker at 19:37 of the first. Brandon leads the series 3-1 and can eliminate Regina with a win at home on Friday.
Connor Hobbs scored on a power play for the Pats in the second, and received a game misconduct midway through the third period. Colby Williams also scored.
ROYALS 5 ROCKETS 4 (OT)
VICTORIA — Greg Chase breathed life into the Royals with an overtime goal to lift Victoria over Kelowna 5-4 and stave off elimination in their second-round series.
Jack Walker scored twice and Austin Carroll and Brandon Magee rounded out the attack as the Royals cut the best-of-seven series deficit to 3-1.
Lucas Johansen, Rourke Chartier, Tomas Soustal and Tyson Baillie had goals for the Rockets, who host Game 5 on Friday.