Bruins-Oilers takeaways: “We absolutely beat ourselves.”

The Boston Bruins had little room for error against the Edmonton Oilers.

They needed all hands on deck against Connor McDavid, Leon Draisaitl and company. That meant no shifts off for Taylor Hall — who found himself benched in favor of Jake DeBrusk in the closing moments of Tuesday’s 3-2 win over the Ottawa Senators. It also meant a stout defensive effort for Boston’s inconsistent blue-line.

From the potent top line to the last defensive pair, Bruce Cassidy needed a cohesive 60-minute effort from his squad.

For two periods, the Bruins limited the damage. Certainly, they encountered a pair of hiccups attempting to extend their leads after Evan Bouchard and Zach Hyman countered David Pastrnak’s first-period tally and Brad Marchand’s second-period mark a mere 44 and 24 seconds after Boston’s respective tallies. Yet, they found themselves in the driver seats after Brandon Carlo blasted home his first of the season late in the middle stanza to give the Bruins a 3-2 lead.

The Bruins developed good habits through the first 40. They didn’t carry over those traits in the final 20.

A costly Carlo turnover led directly to Draisaitl’s stick as he netted the equalizer. The 2020 Hart Winner struck again 3:04 later, tipping home Codi Ceci’s feed in front for the go-ahead tally.

A desperate Bruins bunch garnered a handful of quality scoring chances. But they fell victim to Nick Foligno hitting the post on a breakaway, Pastrnak missing an open net and a Jake DeBrusk tip attempt going just wide. Ceci delivered the back-breaker with 2:19 left, firing home his first of the year from the point past a sprawling Linus Ullmark to secure Edmonton’s 5-3 win.

“We absolutely beat ourselves,” Cassidy said, “100 percent.”

Here’s what we learned following Boston’s first home loss at TD Garden in 2021-22.

Cassidy and Carlo take ownership after third period meltdown

The Bruins didn’t perform all that poorly against McDavid, holding him to one point. But the Bruins beat themselves, as Cassidy alluded to, as their attention to details got away from them.

Surely, Cassidy and his coaching staff aren’t responsible for the turnovers, decision-making with the puck and defensive breakdowns on the ice. On the other hand, the untimely line changes, notably a first-period switch with Marchand that led to Bouchard’s second goal of the season, fall on their shoulders. Yet, Cassidy felt whatever message he delivered didn’t resonate with his team in their attempt to close out a potential marquee early-season victory.

“I gotta do a better job,” Cassidy said. “The mistakes we made, line changes and puck management was a little different. The way we brought pucks out was just…the team beats itself, that’s on us as a staff. We have to do a better job getting them ready to play and understanding what it takes to win. The lack of not shooting, it’s 100 percent on us. We just have to get that point across because we’re not good enough to make some of the plays we’re trying to make. So that’s on us to make sure we’re playing the right way and having our best chance to win.”

Perhaps the coaching staff could do more to get their message across. But the players also share the onus. They’re the ones failing to clear pucks out of danger, missing defensive assignments and committing costly turnovers.

The Bruins couldn’t afford those mistakes with their thin defensive depth. This time, a usually reliable Carlo turned those mistakes into a pair of costly goals on Draisaitl’s tying and go-ahead markers.

“Just one of those nights,” Carlo said. “Third period was one of the worst ones I had in my initial career. Overall, you’ve got to take it and learn from it. But yeah, things just got away from us a little bit and I didn’t respond very well. But overall, it was a great learning experience.”

Encountering learning experiences two months into a new season isn’t terrible necessarily. The Bruins need to turn those lessons into consistency as the year progresses.

The overthinking continued

Edmonton’s speed and skill left little room for thought whenever their opponents have the puck. Even if they allow extended possession, the McDavid and Draisaitl-led counterattack can strike at any given moment.

The Bruins needed quickness, not passiveness, with their attacking zone decisions. They developed quality scoring chances against Miko Koskinen yet only fired 28 shots on net.

Aside from their six-goal outburst against the Red Wings, the Bruins struggled to light the lamp consistently across their four lines. At times, all four lines opted for the perfect play instead of firing pucks toward the net.

The remedy sounds simple. But the theory isn’t easy to execute when things aren’t clicking. Somehow, Pastrnak and company need to return to their shooting roots, especially when they encounter pivotal moments of a given tilt.

“We passed [on opportunities] a little bit, and that’s definitely unacceptable, especially at crunch time,” Pastrnak said. “We have to get a shooting mentality in our head and be a little more aware of the situation and score.”

The top line factored into all three of Boston’s tallies. Yet, even they hesitated at times with their decision-making in the attacking end.

The Marchand-Bergeron-Pastrnak trio will eventually regain their consistency. But they may need to carry the offensive load again until Don Sweeney acquires some outside reinforcements.

The secondary scoring issues have returned

David Krejci’s departure for his native Czech Republic left a significant secondary scoring hole. But Boston’s early-season secondary scoring woes go beyond filling Krejci’s second-line center void.

Boston’s depth forwards hardly generated many quality looks aside from a returning Foligno hitting iron on a breakaway and DeBrusk’s tip attempt going wide.

Marchand, Bergeron and Pastrnak accounted for 12 of the team’s 29 shots on net. All six of Boston’s blue-liners fired at least one shot on goal. Yet, the second, third and fourth lines accounted for nine shots on goal, with DeBrusk, Curtis Lazar and Tomas Nosek each firing zero pucks at Koskinen.

Cassidy assigned the fourth line of Nosek, Lazar and a returning Anton Blidh against Edmonton’s top trio of Hyman, McDavid and Jesse Puljuarvi. They held their own in a difficult assignment, with the Marchand-Bergeron-Pastrnak trio also chipping in.

The second and third lines could’ve built off that with an effective counterattack. For the most part, they once again failed to impress.

The secondary scoring concerns won’t disappear anytime soon. Perhaps Cassidy will change things up again with the second, third and fourth lines ahead of Saturday’s matchup against an improving New Jersey Devils bunch. For now, they’ll have to find a spark outside of the top line from within.