That little crack was all St. Louis needed to put another dent in the Blackhawks' bid for a second straight Stanley Cup title.
Seabrook's blow to the head of David Backes led to a 6-on-4 power play for St. Louis that ended with Tarasenko's tying goal with 6.4 seconds left in regulation, and low-scoring defenseman Barret Jackman ended the game with a drive through traffic, giving the Blues their second straight 4-3 overtime victory over the Blackhawks and a 2-0 series lead.
''Those seeing-eye shots, I couldn't believe it went in,'' Blues coach Ken Hitchcock said.
St. Louis took the opener in triple-overtime and fought off a Chicago rally in a game that began less than 39 hours later. Game 3 is Monday night in Chicago.
Blackhawks goalie Corey Crawford tossed his equipment around in the locker room before meeting with reporters. He said he was screened a bit on the game-winner, adding, ''I had my pads together, but there was a little space there and it just kind of squeezed through.''
Addressing the tying goal, Crawford said: ''It's frustrating, but whatever. I'm not going to cry about it. We've just got to work harder.''
Jackman is the longest-tenured Blues player in a career dating to 2002, and totaled three goals and 15 points in the regular season. He has two career playoff goals, both in overtime and both giving the Blues a 2-0 series lead, also stunning the Kings in the first round in 2012 - although the Kings recovered to take four straight.
''We were taking some big hits and kept our composure,'' Jackman said. ''And in the end, one squeaks in.''
St. Louis rallied after Seabrook received a five-minute major and game misconduct penalty for his hit on Backes that could lead to a suspension for one of Chicago's top defensemen. The Blues captain had to be helped off the ice, went straight to the locker room and did not return for the extra period.
''I have no thoughts on the hit, that's up the league,'' Hitchcock said. ''How do you think he is? Not great. Let the league deal with it.''
Seabrook said he wasn't trying to hurt Backes.
''I feel bad seeing a guy like that on the ice,'' Seabrook said. ''I've been there myself. I wasn't trying to target his head or do anything like that.''
Blackhawks coach Joel Quennevillle didn't want to comment on the hit until he had taken a closer look. At the time, he was worried about the game situation.
''We're almost through it and I was like 'Oh, my God,''' Quenneville said. ''I was more worried about killing the major.''
Instead of retaliating, the Blues stuck up for Backes by sticking to the game plan.
Shattenkirk said repercussions from the hit are ''not for us to focus on.''
''We really have to keep just pushing forward,'' he added. ''Whatever happens, just keep a positive mindset, a clear mind.''
Tarasenko's second goal of the series was a wrist shot that banged off the right post and in. Kevin Shattenkirk had a goal and two assists for the Blues, who also got a goal from Chris Porter.
Duncan Keith, Seabrook and Michael Rozsival scored in a span of five shots to put the Blackhawks up 3-2 early in the third. But Seabrook's penalty proved costly and the Blackhawks got no help from a power play that went 0 for 4 and is 0 for 9 since Seabrook scored on their first chance in Game 1.
Tarasenko made the most of the Blues' 6-on-4 advantage after pulling goalie Ryan Miller.
Keith's goal late in the second ended a scoring drought of 119 minutes and 27 seconds for Chicago since a three-goal first period in Game 1. Before Chicago's rally, Miller stopped 53 consecutive shots.
A Blues checking forward started the scoring for the second straight game. Porter had one assist in 22 regular-season games.
St. Louis made playing to the whistle pay off, capitalizing on a late flurry when Shattenkirk's slap shot from just inside the blue line beat an out-of-position Crawford with 1.8 seconds to go in the first.
NOTES: Quenneville and Falcons offensive line coach Mike Tice are co-owners of a thoroughbred, Midnight Hawk, that was the prohibitive favorite but lost by a nose in the Illinois Derby on Saturday. ... Shattenkirk had a career-best 10 goals in the regular season. ... Porter, a ninth-round pick of the Blackhawks in 2003, scored his first goal since April 7, 2013, at Detroit. ... Alexander Steen, who got the game-winner in triple-overtime in Game 1, is among five Blues players with two overtime playoff goals. The others: Brett Hull, Pierre Turgeon, Scott Young and Mark Reeds.