If it's any solace to the St. Louis Blues, the Boston Bruins feel (some of) their pain.
But the replay showed Karlsson scored after a pretty obvious hand pass from teammate Timo Meier.
So, why didn't the officials on the ice (or the situation room in Toronto) review the goal to check for a hand pass? Here are the postgame explanations from NHL series director Kay Whitmore and the league office:
Pool reporter: Did any of the officials see it?— Jeremy Rutherford (@jprutherford) May 16, 2019
Whitmore: "It's a non-reviewable play. You can read between the lines. You can figure out what you want. You watched the video. But it's just non-reviewable. I know that sounds like a cop-out answer, but that's the truth."
The official word from the NHL: "Plays of this nature are not reviewable. A hand pass that goes into the net can be reviewed but a hand pass between teammates cannot be reviewed."— Greg Wyshynski (@wyshynski) May 16, 2019
Feeling some déjà vu, Bruins fans? The B's were victimized by the NHL's apparently arbitrary review process in Game 4 of their second-round series with the Blue Jackets, when Columbus' Artemi Panarin scored just seconds after the puck deflected into the protective netting for what should have been a stoppage in play.
The missed call and non-review didn't cost Boston, which went on to win 2-1 en route to a series victory. But goaltender Tuukka Rask said something after the game that make him look like Nostradamus after Wednesday night.
"In this day and age I think it's crazy that, you know, if the refs don't see it, why the league can't call … I mean, they're watching the game, right?" Rask said at the time.
"I mean, what if that's in overtime, you know? It didn't cost us, but I think it's just funny that they can look at a lot of other goals going back and calling back, so why not that?"
HAGGERTY: Red-hot Rask can carry B's to the Cup
Rask's nightmare scenario became a reality for the Blues, who like Rask were left wondering why the heck the NHL can review a potential offsides 30 seconds before a goal but not an obvious hand pass that leads directly to a game-winning score in the Western Conference final.
St. Louis Blues captain Alex Pietrangelo on hand-pass:— Greg Wyshynski (@wyshynski) May 16, 2019
"I really didn't get an explanation other than I guess there's a different set of rules for two different teams, so I'm sure they'll lose some sleep tonight after looking at it. But that's all I'm going to say about it."
After two controversies in the Stanley Cup Playoffs about reviewable plays, expect the NHL to take a look at its rulebook this offseason.