BOSTON — Ten of the 12 forwards who suited up for the Boston Bruins in Monday’s preseason game against the Philadelphia Flyers are locks to be in the opening night lineup a week from Wednesday in Washington.

The top line of Mogan Geekie, Elias Lindholm and David Pastrnak isn’t going to change. The second unit of Pavel Zacha, Casey Middlestadt and newcomer Viktor Arvidsson likely won’t, either. The fourth line is pretty set in stone with Sean Kuraly centering two guys who didn’t play Monday: left wing Michael Eyssimont and heavyeight Mark Kastelic on the right.

That leaves the third line, which on Monday night featured the trio of Matej Blumel at left wing, Fraser Minten in the middle and Matt Poitras on the right side.

Tanner Jeannott, a 28-year-old power forward the Bruins signed to a five-year deal, $17 million dollar deal in the offseason, will almost assuredly cement himself on the portside of that third unit. At 6-foot-2 and 221 pounds he brings the muscle, NHL know-how and locker room experience the organization was looking for.

Who Jeannott will ultimately skate with remains a mystery … or at least rookie head coach Marco Sturm isn’t ready to reveal his cards on that decision just yet.

The Blumel-Minten-Poitras line had their moments against the Flyers. They all bring different skill sets to the table, with Blumel — who had an American Hockey League-leading 39 goals for the Texas Stars a year ago — the triggerman of that group; Minten the youngster who shows veteran tendencies on ice, and Poitras an enigmatic talent who is still trying to make his mark in Black-and-Gold.

All three have played in three of Boston’s four preseason contests, and Sturm said they’re likely each to play one more before any decisions on their immediate futures are made.

“They practice so hard and so well the whole time, but I feel like in games they think too much,” Sturm said. “I have to get them out of that (mindset); don’t think, just play the game. It’s a tough league, but it’s even tougher when there’s a lot going on in your brain. I just want them to play free.”

The 21-year-old Minten was the visible standout among the trio Monday night. Poised with and without the puck, the former Toronto Maple Leaf, traded to Boston at the deadline last March, dished out four hits and won half of his eight faceoffs. The 6-foot-2, 2065-pound left shot also earned some time on the penalty kill and is capable of playing the wing as well as center.

You get the sense that the Boston brass desperately wants Blumel to make the club out of camp. With the puck on his stick in and around the opposing net he’s certainly of capable of being an everyday player, but away from the net or without the puck he’s still a work in progress. Sturdy at 6 foot and 202 pounds, he can generate chances for himself, a plus on a team without a lot of scoring pop. Blumel also showed a willingness to get in the forecheck against Philadelphia.

Poitras has played 66 games in Boston over the last two seasons but has just six goals to show for it. The former second round pick is probably better suited as a center than a wing, where his 6-foot, 189-pound frame has difficultly sustaining wall work against much bigger, strong defensemen. He did, however, draw roughing penalty against the Flyers’ Emil Andrae in front of his own bench Monday, showing that willingness to battle for the puck and space for himself.

Pastrnak, one of team’s elder statesmen, watched the three of them closely from the bench Monday and said it was fun watching them do their thing.

“Minty is so mature for his age; his defensive play and decision making for how young he is, it’s very impressive,” said Pastrnak after the 3-2 shootout loss. “Posty (Poitras) and his line were a big reason why Geeks (i.e., Morgan Geekie) scored a goal; they had a great shift right before.

“It’s the perfect opportunity; there are open spots on this team,” Pastrnak added, “and it’s fun to see them still come to the rink with a smile, but they also know and recognize they have to play with heart.”

Marat Khusnutdinov, Fabian Lysell, Alex Steeves, Patrick Brown and several others would all love to have one of those coveted 13 forward spots that Blumel, Minten and Poitras are also fighting for. Who winds up putting on the white away sweater in Washington opening night will be determined within the next week.

Phil Stacey, the Executive Sports Editor of The Salem News, covers the Boston Bruins for CNHI Sports Boston. Contact him at pstacey@salemnews.com and follow him on X @PhilStacey_SN