Derek Roy blew a chance to end the game in the first minute of overtime.
Then St. Louis coach Ken Hitchcock gave him a chance to make up for it.
Roy scored once in regulation and added the clincher in the fourth round of the shootout on Thursday night to lead the Blues to a 3-2 victory over the Boston Bruins.
Roy, who hit the crossbar on a breakaway in sudden death, didn't make the same mistake when he got another chance to win it.
"I usually look at body language on the bench, and Roysie was perked up he wanted to go," Hitchcock said. "So we had him go."
Jaroslav Halak stopped 27 shots in regulation, two more in overtime, and three in the shootout as St. Louis won for the fourth time in five games and continued the hottest start in its history.
David Backes also scored for the Blues, and NHL points-leader Alexander Steen converted their other shootout goal after going the entire game without a shot.
Gregory Campbell and Carl Soderberg scored for Boston. Tuukka Rask made 24 saves and forced Roy to put one off the crossbar on a breakaway in the first minute of overtime.
"I knew I could get him on that shot, and I thought I picked it perfect, and I hit crossbar," Roy said. "I wanted to redeem myself in the shootout, and Coach put me out there. ... It shows that he's got confidence in me going out in the shootout.
"I just wanted to help my team win the game, and I'm happy to do that and be put in that position to do that."
Soderberg broke in alone in the last 15 seconds of overtime, but he meekly shot the puck into Halak's pads just before the final buzzer.
That sent the game to a shootout, and Boston took an early lead when Patrice Bergeron beat Halak over his shoulder to make it 1-0. T.J. Oshie, David Krejci and Jarome Iginla all missed before Steen poked it through Rask's pads to tie it 1-1 after three tries apiece.
Chris Kelly missed for Boston in the first extra round, and Roy went in quickly, skidded to a stop and then went around Rask to poke the puck in for the winner.
"He told guys on the bench that he was going to do the move, and did it and got away with it," Hitchcock said.
After Roy's shot went in, Rask slammed his stick against the goal post and continued hammering it into the ice as he skated off to the locker room.
It was the Blues' 15th win in 21 games this season, giving them 33 points — the most in the NHL. The Bruins had won six of their previous seven games and taken over the best record in the Eastern Conference.
"There's a lot of similarities" between the teams, Backes said. "I don't know if we quite have a 6-foot-9 defenseman, but there's tough to play against forwards, and teams that are disciplined and stick to the game plan.
"You saw a couple of breakdowns tonight, and they all ended up in the back of the net."
Each team had just one penalty in the game, and Bruins coach Claude Julien said he thought his team played well enough to win.
"I thought it was a real fun game to watch," he said. "Everything, from my end, except for that extra point that I thought we should have had."
The Bruins scored late in the first when Blues defenseman Ian Cole fell in his own end, allowing Boston to keep the puck in the zone. Torey Krug slid it over to Campbell, who tried to one-time it, but sculled it off the heel of his stick. The slow-moving puck seemed to confuse Halak and went into the net off the corner of the post.
But the Blues tied it just 37 seconds later, when Roy wristed the puck toward the net from the left point. Stewart tried to deflect it near the circle, missing the puck but knocking a defender's stick away. Another Blues player tried to get a stick on it in the crease but it also eluded him as he was taken down by Boston defenseman Matt Bartkowski.
Instead, the undeflected puck went right through Rask's legs to make it 1-all with 9 seconds left in the period.
St. Louis took a 2-1 lead late in the second when Kevin Shattenkirk's wrist shot from the point was deflected into the net by Backes. It was Shattenkirk's 100th career assist.
This time it was the Bruins' turn to answer quickly.
About 2½ minutes after the Blues took the lead, Reilly Smith fed the puck from behind the net to Soderberg in the slot, and he beat Halak to tie it 2-2.
NOTES: Hall of Famer Bobby Orr took part in a ceremonial puck drop. John "Pie" McKenzie, another member of the Bruins' 1970 and '72 Stanley Cup championship teams, was also in attendance. The 1970 team swept St. Louis in the finals. ... The Bruins called up D Kevan Miller to fill in while Adam McQuaid and Dennis Seidenberg are out with undisclosed injuries. Miller made his NHL debut. ... St. Louis finished a three-game road stretch. The Blues split the first two, losing to Washington and beating Buffalo by 4-1 scores. ... The first penalty of the game was called with 1:54 gone in the third period. ... Steen entered the night tied for the NHL lead with Pittsburgh's Sidney Crosby at 26.