By Chris Emma–

CHICAGO (CBS) — Walled away in that chamber of doom, Andrew Shaw was penalized for two minutes to last a lifetime.

Hockey’s sin bin offers quite the quarters for reflection. Shaw committed the boneheaded interference penalty with 2:04 remaining, it coming on a mindless shove, and was left to think about it for what must have felt like ages. His Blackhawks seeking a comeback in Game 4, Shaw’s side was sent down a man trailing 4-3. The Blackhawks couldn’t prevail, with that final score holding for a win by the Blues that put them up 3-1 in their first-round series.

“You can’t take that penalty,” Blackhawks defenseman Duncan Keith said.

Four games of playoff hockey have each been decided by a goal. The Blackhawks and Blues have laid it all on the line. Yet, a key difference in this series has been discipline.

It’s not the Blues — a team bounced in three straight first rounds — that are making the unnecessary mistakes. It’s the defending Stanley Cup champion Blackhawks who can’t get out of their own way.

On Tuesday, St. Louis scored on two power plays, with the terrific Vladimir Tarasenko scoring late in the second period and Jaden Schwartz getting one early in the third period. Where’s that outstanding Blackhawks’ penalty-kill unit that’s come through time after time before?

The game really drifted away from the Blackhawks midway through the third period when second-year defenseman Trevor van Riemsdyk turned the puck over to Blues winger Alexander Steen, who hurled it past Corey Crawford. That created a rare two-goal lead that this series has seldom seen.

Shaw’s horrendous gaffe would be the final dagger for the Blackhawks, who couldn’t muster any chance of the game-tying tally.

Historically, it’s been the Blues making the egregious mistakes in key moments, leading to early exits and disappointment for Ken Hitchcock’s club. Now, it’s the Blackhawks making those costly errors and the Blues showing resiliency. They were twice down 2-1 at the United Center and left with a pair of road victories.

“We just have a belief that we can beat anybody,” Hitchcock said.

Entering this hotly contested first-round series between the two Central Division rivals, one wouldn’t have expected it would be the Blackhawks playing undisciplined hockey and the Blues appearing unflappable. But here we are, with Chicago a game away from the end of its Stanley Cup defense.

Sixty minutes could keep the Blackhawks from repeating as champions. They tout their “next level,” and showed it at times in Game 4, but it wasn’t enough to beat the Blues.

What do the Blackhawks need to do better in Game 5?

“Play with some heart,” coach Joel Quenneville said. “We’ve got to be disciplined. Play the right way. We got to be stingy.”

Doubting the Blackhawks has proved to be foolish in the past. The Core has come through with countless clutch moments, leading to three titles in six years. Chicago has even overcome a 3-1 deficit before, battling back against Detroit in 2013 and winning in overtime of a Game 7 at the United Center.

But to stack the odds further against the Blackhawks, they face the 3-1 hole and the Blues own home-ice advantage, with two of the last three games in St. Louis. Game 5 is Thursday.

“It is what it is now,” Keith said. “We got nothing to save it for now, that’s for sure.”

Their decorated past would suggest not to count out a series comeback from the Blackhawks. Of course, they’ve never played with such poor discipline before.

The Blues are playing their game, bringing the physical presence to the Blackhawks’ finesse style. This time, though, it’s St. Louis that’s more polished. In a series of evenly matched games, discipline and some puck luck have made the difference.

Following the final horn, the Blackhawks and Blues reconvened in front of St. Louis goalie Brian Elliott’s net and brawled some more. The game was lost for the home side, but the slugfest continued. Then, both teams regrouped and retreated to their dressing rooms.

A pin drop could be heard in the Blackhawks’ postgame scene. It would’ve taken a clumsy reporter stepping on the roped-off logo to bring any bit of noise.

The Blackhawks’ reflections on a brutal loss began somewhere after Shaw took to the penalty box for two minutes that seemed like forever. They carried into the dressing room for more of that disbelief.

It’s do or die for the Blackhawks, whose backs are square against the wall. More than ever, it’s desperation time for the defending champs.

“No pressure,” Quenneville said. “Go try to win one game and come back here for Game 6. That’s got to be the mindset.”

Chris Emma covers the Chicago sports scene and more for CBSChicago.com. Follow him on Twitter @CEmma670 and like his Facebook page.