CHICAGO -- With their Stanley Cup Playoff lives on the line, the St. Louis Blues were given an opportunity to force Game 7 in their Western Conference First Round series against the Chicago Blackhawks.

Knotted in a 1-1 tie during Game 6 on Sunday, the Blues had just peppered the Blackhawks with 17 second-period shots, and after being given two first-period power plays, St. Louis had a chance at four more of them in the second period at United Center.

Nearly the entire second period was spent in the Blackhawks zone, and the Blues had chance after chance. But when those opportunities went by the wayside, Pandora's Box was opened and the Blues were once again left on the outside looking in.

Chicago's third-period blitz saw the Blackhawks do something the Blues failed to do multiple times: score on the power play. Chicago captain Jonathan Toews gave the Blackhawks a lead 44 seconds into the third and it led to a four-goal outburst in a 5-1 victory that eliminated the Blues for the second postseason in a row in six games after taking a 2-0 series lead.

The Blues were their own worst enemy when they scored 10 goals in six games against the Los Angeles Kings in 2013. Not much changed; they scored 14 goals in this series, but were 2-for-29 on the power play. Eight of those 14 goals came in Games 1 and 2, helping the Blues race out to a 2-0 series lead.

"I think the way we played in the first 40 minutes, the game was tilted in our favor," said Blues captain David Backes. "We had quite a few chances, quite a few power-play opportunities we don't capitalize on and you're going into the third period with a 1-1 game in a Game 6 where it's laid on the line. They get a power-play goal and it seemed to have more of an effect on us than probably it should of. There's still 20 minutes to play in a series that's been damn near tied up the whole time. We start pressing a little bit and they get a few chances and they've got plenty of guys who can bury the puck and got to display it there in the third, but all that stuff aside, we didn't get the job done."

And not getting the job done dispatches the Blues from the playoffs for a third straight season, and in the opening round for the second year in a row.

"Yeah, I think it was right there for us," said right wing T.J. Oshie, who scored the Blues goal in the first period. "I don't know what the shots were (17-3), but I thought we were playing very well. And I think we woke up some guys in that third period that were sleeping for their team all series."

One of those players included forward Patrick Sharp, who had gone without a point in five games.

"I think we had a real good feeling going into the third, we made a mistake on the penalty kill," Blues coach Ken Hitchcock said. "We got seamed. Even at 2-1 we're still in good shape. The third goal was really a back-breaker for us. That was really the one that hurt because we've been chasing all series and been able to catch up in games, but the third goal really took the wind out of our sails.

The Blues have been known as a team that will work for success. But the finished product will send them into the offseason wondering what might have been. Consistently not being able to produce at critical times was the biggest downfall.

"I thought we had them," Hitchcock said. "We had a calmness, an intensity and a confidence. We were making plays. The puck was bouncing along the goal line. But you gotta score, you gotta finish, and we didn't finish. The first two periods, we just played. We played the way we can. We played with a real high level of intensity. We didn't have any panic in our game at all.

"I think the players felt really, really good after two periods. We were in a great spot, but we made big errors. We made two big mistakes on those two goals and that hurt us a lot. We can't do that stuff if you're going to win at the end. We cracked a little bit, and that's something you don't want to do."

The Blues also didn't want to head into another offseason of uncertainty, but that's the position they're in.

"It doesn't get any easier," defenseman Jay Bouwmeester said. "Every year you don't make the playoffs or lose in the first round or you lose period, it's just a wasted opportunity. We had, up until the last week or two of the regular season, we had a fantastic year. We had it turned around in the first couple of games, and then had a couple close ones here, a close one back home and then for two periods played pretty well [Sunday].

"They're a good team. They stuck with it and it's the same lesson we learned last year."