The Grizzlies led all the way until Ontario's Brodie Sheahan tied the game with 3:01 left in regulation.
Game 4 was a mirror-image of Friday night's third game, when the Reign scored with 29.3 seconds left and won early in overtime, also by the score of 2-1.
"Just a lot of emotion right now, obviously," said Utah coach Kevin Colley. "I don't want to comment on this series other than to congratulate Ontario on a well-played one."
Once again, Grizzly goalie Shane Owen was superb. He stopped 43 of 45 shots in Game 4, but two Utah turnovers gave the Reign the chances they needed.
Owen "was our most valuable player, hands down," Colley said. "It's too bad we couldn't score more for him. It just unfortunate because he rose to the occasion. He should hold his head up high."
The Grizzlies started well and pressured Ontario goalie Jean-Francois Berube from the opening moments.
Seven minutes into the game, Utah grabbed a 1-0 lead when Adam Estoclet and Jordan Clendenning kept the puck alive along the boards and Jimmy Martin scored.
Martin gained possession near the blue line, stepped around a defender and patiently moved toward the net before rifling home a 35-foot slap shot.
The game stayed 1-0 into the third period, when the Grizzlies had a golden opportunity to seal the deal after Matthew Clune was called for tripping with five minutes left.
Utah nearly scored a minute later, but Tuzzolino's slap shot from the slow was kicked away at the last instant by Berube.
"To tell you the truth, I thought they was going in," Tuzzolino said. "I didn't think there was any way I was missing a slap shot from there. But the goalie reacted and made a nice save."
The Grizzlies' man-advantage ended moments later, when James Martin was called for holding with 3:16 left in the game.
The Reign tied the game only 15 seconds later. Sheahan knocked down down a clearing pass just inside the blue line and flipped the puck over Owens' shoulder, setting up Sheen's game-winner in overtime.
Ontario 2, Utah 1 (OT)
O Ontario sweeps Utah out of the ECHL playoffs with a 2-1 overtime win in Game 4.
• The Grizzlies own a 1-0 lead until the Reign tie the score with 3:01 left in regulation.
• Utah goalie Shane Owen plays well, stopping 43 of the 45 shots he faces.