The Bruins have discovered a flaw in their game: the second-period slump

Bruins coach Jim Montgomery says the second period is "where you can build the most momentum."John Tlumacki/Globe Staff

Any coach can find an area of improvement for his team, no matter how hot the squad.

Boosting their record to 11-2-0 via Monday’s win over the Blues, Jim Montgomery’s Bruins tied Art Ross’s 1929-30 club for the best 13-game start in franchise history. And yet, had they come up with a couple of lockdown second periods, these Bruins might be perfect at this stage.

The Bruins have the league’s best goal differential (plus-22), despite ranking 25th in the second period (minus-2). They are not in good company. Six of the seven teams behind them in that category have losing records, including the five worst records in the league (Ottawa, Anaheim, San Jose, St. Louis, and Columbus).

“Our second periods have not been good throughout the season,” Montgomery said. “I think that’s the period where you can build the most momentum. Our first periods have been good, and usually when you tax a team in the first period, your second period allows you to blow a game open.”

The Bruins typically start well, ranking third in first-period goal differential (plus-9), and no team has closed better (plus-13 in the third period). The midway stretches have been rife with turnovers, particularly at the offensive blue line. A pair of turnovers in Monday’s win led to St. Louis breakaways.

One culprit was the ever-present long change; since teams alternate the end of the ice they’re defending every period, a home team has to skate farther to its bench during the second. Bad breakout passes and turnovers can leave tired players unable to get off the ice.

But Monday’s third period was much better for the Bruins, who cleaned up their game and scored twice to seal a 3-1 win.

David Pastrnak noted that turnovers will happen, especially for a team that likes to make plays.

“A lot of our wins were tied going into the third period and we end up winning them,” Pastrnak said. “You find a way to win those games and you build up your confidence a little bit as a team, and you know what to do to get those wins in the third. Sometimes knowing you can is big.”

Time management

Among the third-period adjustments Montgomery made Monday: He benched Jakub Zboril.

With the defenseman fighting the puck and a three-day break between games ahead, Montgomery played five defensemen for the third period. Hampus Lindholm (25:36) and Connor Clifton (25:34) played nearly half of the period, while Matt Grzelcyk and Brandon Carlo finished in the 20-minute range.

“I wanted to ride the horses,” Montgomery said. “We have a deep D corps without [Charlie] McAvoy and [Derek] Forbort that are playing really well that we can go down to five to try to win a game.”

Late in the second, Montgomery sparked his attack by moving Pavel Zacha to play with David Krejci and Pastrnak, and putting Taylor Hall with Charlie Coyle and Nick Foligno. He also found ways to use his fourth line, which rewarded him.

Even though St. Louis wasn’t playing its fourth line often, the Bruins rolled out Trent Frederic, Tomas Nosek, and Craig Smith for a regular turn in the third period. Frederic’s goal with 3:32 left all but sealed the win.

Frederic celebrates his third-period goal with teammate Craig Smith Monday night at TD Garden.Brian Fluharty/Getty

“I wish I could have gotten them more minutes last night,” Montgomery said of the group, led in ice time by Nosek (10:51). “But they stuck with it, and their mental strength through not playing through long stretches of the game and being able to help us win was really important to the team’s success.”

Still under contract

Mitchell Miller remained under contract with the Bruins as of Tuesday’s waiver deadline. Meanwhile, his agent pushed back on Cam Neely’s assertion that “new information” caused the team to cut ties with the prospect Sunday.

“To the best of my knowledge, there’s no new information,” Eustace King of O2K Sports said in an episode of the Cam & Strick Podcast posted Monday.

The Bruins’ options include carrying Miller’s contract and then buying him out at one-third of his salary next summer; waiving him for purposes of termination (a move that would surely draw a Players Association grievance); and working with Miller, King, and the NHLPA to find a settlement.

King, promoting his client, said Miller and the middle-school classmate he bullied, Isaiah Meyer-Crothers, had recently been in contact as they went through “their own healing process,” and they plan to someday “tell their story together.”

Skating or sitting

The Bruins held an optional practice Tuesday, with Pastrnak, Hall, Jake DeBrusk, and Foligno among the 13 skaters. Patrice Bergeron, Brad Marchand, Krejci, and Lindholm were among those who took a maintenance day. The goalies (Linus Ullmark and Keith Kinkaid) were spelled by fill-ins Keith Segee (a Massachusetts state trooper) and Erik Mihalik (ex- of Cornell) … Montgomery said McAvoy (shoulder surgery) “still has boxes to check,” while Forbort (hand surgery) may still be three weeks away … Both these Bruins and the 1929-30 edition scored 53 goals through their opening 13 games. The ‘29-30 club finished 38-5-1 in a 44-game season and lost the Stanley Cup Final. The modern club record for points percentage is .776, set in 1970-71 (57-14-7) … New England is PK country, apparently. Boston leads the NHL in penalty killing (93.3 percent). Providence is second in the AHL (87.8). Maine is fourth in the ECHL (90.9) … The Bruins and P-Bruins (8-1-1) are a combined 19-3-1.