Matt Niskanen’s role in the Capitals’ blue-line corps has steadily grown. (Toni L. Sandys/The Washington Post)

Of all the deals Brian MacLellan has made in his three years as the Washington Capitals’ general manager, there’s one for which he gives himself an especially firm pat on the back. It wasn’t that flashy swap for T.J. Oshie or the coup of signing Justin Williams. He sent a message to his team of being all-in this season after acquiring Lars Eller and then Kevin Shattenkirk, and while those trades were savvy, neither is the move in which he takes the most pride.

MacLellan has earned a reputation for his big moves, but one of his first is still his favorite. Signing defenseman Matt Niskanen to a seven-year contract wasn’t as lauded as some of MacLellan’s other deals, but it was the first step to the Capitals becoming a perennial contender with an improved defense.

“He’s just everything you want, you know?” MacLellan said. “Good two-way guy, good teammate, competitive every night. He’s exactly what you’d want in a defenseman.”

Before Niskanen landed in Washington prior to the 2014-15 season, it was a different deal that saved his career. As the Capitals open their second-round series against the Pittsburgh Penguins on Thursday, Niskanen is once again pitted against the team that put him on the path of becoming Washington’s top blue-liner.

“That’s one that certainly puts a smile on my face to talk about,” associate coach Todd Reirden said.

A first-round pick by the Dallas Stars in 2005, Niskanen made the team after his first training camp, impressing with a plus-22 rating in his rookie season. “Maybe it went a little too well,” Niskanen said. His play steadily declined in his third and fourth years in the league, and in 2010-11, he had played in 45 games with no goals, six assists and a minus-one rating. As the Stars dealt forward James Neal to Pittsburgh for defenseman Alex Goligoski, Niskanen was included as a throw-in.

Niskanen knew his career was at a crossroads at that point. Dallas had something invested in Niskanen as a high draft pick, but the Penguins had less stake in him succeeding. The trade would either serve as the fresh start he needed, or it would be the beginning of the end for his time in the NHL. Reflecting on the move now, Niskanen said he “hit the jackpot.”

“I was in the dumps,” he said. “I was within a season away of going down to the minors probably.”

Defenseman Brooks Orpik was playing for the Penguins at the time and remembered initially thinking the trade was a straight swap of Goligoski for Neal. “I think Dallas wouldn’t make the trade unless we, in their opinion, took Niskanen’s contract off their hands,” Orpik said.

As an assistant coach on Pittsburgh’s staff at the time, Reirden worked primarily with the blue line, and Niskanen’s first day with his new team involved a skate with Reirden and Orpik. By the end of it, Orpik was chuckling as he approached Reirden.

“I was kind of just laughing that this was the sort of throw-in we had to take off their hands after seeing how talented he was just in that first 45 minutes,” Orpik said. “The way he could skate, the way he could handle the puck and shoot the puck, I don’t know if you’d say it was too good to be true, but we definitely probably got the better end of the trade.”

In Dallas, Niskanen had been in and out of the lineup, but in Pittsburgh, he started as the team’s sixth defenseman. Reirden devoted time to working with him individually and assigned him a new challenge to work toward every year. Niskanen kept meeting those, and his responsibility and time on the ice climbed with each season, as did his production. His confidence was steadily rebuilt, and in his last season there, he had a career year with 10 goals and 36 assists while averaging more than 21 minutes per game in a top-four role.

“Mentally, I told myself, okay, either I can do this or I can’t,” Niskanen said. “I kind of approached it where I don’t care kind of what external things happened. I’m just going to go as hard as I can and let the chips fall. I tried to bring a daily work ethic where I tried to focus on small, little victories every day and work on my game and habits and it kind of grew over a period of time.”

After that 2013-14 season, he felt his next new challenge was a change of scenery, so along with Orpik, he followed Reirden to Washington. By that point, Niskanen was “mentally in a lot better place,” he said. Coach Barry Trotz was in his first year with the Capitals, and he credited Niskanen and Orpik for helping to change the culture of the team that season through the example of their everyday professionalism.

Niskanen is a puck-moving blue-liner with offensive upside, but it’s his consistency and sound positioning in the defensive zone that’s praised most. Trotz has said there’s no “arrogance” in his play: he’s not flashy, but is seemingly always aware of what the right decision is in any situation. This season, he was put in a mentorship position with a new defense partner in young Russian Dmitry Orlov. They’ve become Washington’s best duo, expected to draw the most challenging defensive assignment this series in limiting star Penguins center Sidney Crosby.

“To see it go completely full circle has been certainly fun to watch and fun to be a part of,” Reirden said.

“When things are going really bad,” Niskanen said, “in the future, then you appreciate how good the good times are.”