Boston left wing Cole Koepke, center, celebrates his goal against the Montreal Canadiens on Oct. 10. Stuart Cahill/Boston Herald

The Boston Bruins made a big splash in free agency last summer, hauling in some players they thought would be high impact players.

Cole Koepke was not high on that list.

But through the first five games of the season, Koepke – signed by the Bruins to a one-year deal for the $775,000 league minimum – stands out as the team’s most pleasant surprise. A sixth-round pick of the Tampa Bay Lightning (183rd overall), the 26-year-old Koepke toiled for three-plus seasons in that organization, playing only 26 games for the big club, and managing just a goal and an assist.

Yet after earning his spot on the roster and in the lineup with a good training camp, Koepke has been part of a “fourth line” that’s not playing like a fourth line. Koepke, with Johnny Beecher and Mark Kastelic, have not just been a spark plug but an engine for offense.

Through the first five games, the line takes up three of the top five spots on the Bruins’ scoring list. Koepke (2-3-5) and Beecher (2-3-5) each have two goals and three assists as well as a team-high plus-9. Kastelic also has 2-3-5 totals. According to Natural Stat Trick, the Bruins have outscored opponents 8-0 in the 39:40 of 5 on 5 ice time the line has seen.

Koepke scored the first goal in Boston’s 5-3 win over the Colorado Avalanche on Wednesday.

“He’s been a great surprise, (though) I don’t think he’s been that much of a surprise to our pro scouts that recommended him and spoke highly about. And he’s rewarding those scouts and us with the effort and how he’s playing,” said Coach Jim Montgomery.

Asked earlier in the season why he thought Koepke hadn’t been able to stick in the NHL before, Montgomery theorized that for some players, like Koepke, can take a while to adjust to a bottom-six role after occupying a top-six spot in college. Koepke was part of  Minnesota Duluth NCAA title teams and was relied upon to score goals for the Bulldogs.

“I think there is some truth to that,” said Koepke, who had two 20-goal seasons for Syracuse in the AHL. “Coming from college, you play top six and it was a lot of the same players, and you get more and more comfortable. Sometimes when you play more minutes, it’s easier to get into a groove. But I think this bottom-six role was something I knew I could fit in and you just have to find a way if you’re not playing as many minutes to still have a positive impact on the game. I think coming in here with the staff and the systems, and the guys have really helped me, and it’s something I’m getting more and more comfortable with and I’m happy to do.”

Montgomery is leaning more and more on the line. In the win in Colorado, that line was up every time after the Avalanche scored a power-play goal, three in all, and the trio did a good job of stemming any Avalanche momentum. All three players got over 13 minutes of time, with Kastelic topping out at 16:21. The “third line” of Max Jones, Matt Poitras and Riley Tufte played fewer than 10 minutes.

They consistently play below the other team’s goal line. Late in Wednesday’s game with the Bruins nursing a one-goal lead, Montgomery matched them up against the Nathan MacKinnon-Mikko Rantanen line and shut it down. The group was also on the ice for Colorado’s 6 on 5, leading to Beecher’s empty-net goal.

“We not only as a team have an identity but I think us three know what we want to accomplish out there,” said Koepke earlier this week. “We’re building chemistry more and more in practice, and then games are more comfortable, playing together, staying connected and playing fast and hard, and creating an identity of just wearing teams down, managing the puck well and just being a line that the coaching staff and the team can trust when we’re out there, regardless of the situation or matchup. That’s something that we want to just keep building.”

While goals have been coming for the line early in the season, the trio doesn’t necessarily have to score to do its job.

“We always want to go out there and create momentum, create energy and wear teams down,” said Koepke. “If it’s in our zone, we want to be defensively sound. We want to advance the puck in their end and get down the other end. That’s where we do our thing and use our size and our speed to wear them down. It doesn’t have to be directly related to goals to have a positive impact. It’s really nice when you put in that work and the points for our line come. But you can make impacts other ways and we’re always going to try have a positive impact on a game.”

By nature of being a fourth-liner, nominally at least, players are always spurred by competition from below. There are players looking to make their own foothold and the fourth line is their first rung to grab. Koepke understands that.

“There’s always going to be competition,” said Koepke. “This organization has so many good players, whether they’re here or in Providence. Everyone’s trying to make it to the NHL and a lot of times that first step is coming in on the fourth line and getting comfortable and growing from there. You can just never be comfortable in your spot and think it’s always going to be there for you. You have to come in and earn the opportunity and put in the work to get better every day.”

So far, Koepke and his linemates have look like they’re anything close to comfortable in their spots. And that’s served them – and the Bruins – well.