BOSTON -- Few teenagers could make their debut during the Stanley Cup playoffs and fit right in.

But 19-year-old Charlie McAvoy has done just that for the Boston Bruins.

With their blue-line lineup depleted because of injuries, the Bruins signed McAvoy, who had just turned pro after completing his sophomore season at Boston University, last Monday. Two days later, he made his NHL debut in Game 1 of Boston's first-round Eastern Conference series against the Ottawa Senators.

McAvoy, a first-round pick (14th overall) in 2016, has been outstanding in his first two games for the Bruins, averaging 25 minutes of ice time.

"There's not a lot to pick on in Charlie's game," said Bruins coach Bruce Cassidy.

McAvoy's composure and confidence stand out, and he has already showed that he's not afraid to jump into the play. Scouts compare McAvoy's skill set to that of Nashville Predators star P.K. Subban, another mobile, right-shooting defenseman. The Bruins envision McAvoy having an impact in all three zones with his hockey sense, speed and ability to control the play.

McAvoy will likely deal with the inevitable ebbs and flows that all rookies do at some point. But the small sample size of his play so far is a strong indication that he has a promising future in the league.

"What a great pick by [the Bruins]. Boston got this one right," said the head of scouting for one Western Conference team. "Once he gets his body into NHL shape, he's the real deal."

After the 6-foot, 208-pound defenseman sheds some of his "baby fat" and transforms his body, he will have an even greater impact for the Bruins. But he's not succeeding by brute force alone. He has shown poise with the puck and sound positioning in the defensive zone.

"He's been a real boost for us," Cassidy said.

Watching McAvoy on and off the ice, it's hard to believe he's a rookie, much less one with only two games' worth of experience. So, how has he remained so calm while stepping into the playoff cauldron?

"It's just hockey," he said. "We've all been playing it since we were 5 years old. It's obviously a different level -- the highest level -- but at the end of the day, it's just the game we all love."

When the Bruins lost two of their top defenders -- Torey Krug and Brandon Carlo -- before the playoffs because of injuries, GM Don Sweeney looked at the organizational depth chart and decided to sign McAvoy to a three-year, entry-level contract. He had been signed to a professional tryout agreement and was playing for the Providence Bruins, but the parent club needed his skill set and felt he was ready.

Along the way, the Bruins also lost defenseman Colin Miller and Adam McQuaid to injuries. Both are listed as day-to-day as the team prepares for Game 3 on Monday at TD Garden in Boston. As the injuries to Boston's blue line mounted, so did McAvoy's minutes.

"It's something I don't even think about," he said of the extra workload. "I'm just trying to be responsible and reliable every shift."

So far, McAvoy's adjustment has been relatively smooth.

"It was a good transition for myself, and there were a lot of teaching points through two games," McAvoy said. "But overall it was good, and I thought I played some good, simple hockey. I'm just trying to do my job."

Charlie McAvoy (73, far left) has fit right in with his Bruins teammates and has already been instrumental on the power play. Sean Kilpatrick/The Canadian Press via AP

Those teaching points included learning the speed of the game at the NHL -- and the need to speed up his decision-making process.

Cassidy has shown no reservations about playing McAvoy in any situation. The rookie has been playing big minutes on the power play, and the only reason he hasn't seen time on the penalty kill is because that unit has been solid all season, and Cassidy doesn't want to interrupt its chemistry. But with Boston beset with even more injuries to its defensive core, McAvoy could see some PK time.

McAvoy has certainly never played this many games in a season in his young career. After BU's season ended, and before he decided to turn pro, he thought he would be taking a break. The sudden need to ramp it up again came as a shock.

"It was definitely weird," he said. "In my mind, my season was over. I was done, and it was kind of my offseason. Then, as soon as I made the decision [to turn pro], I'm in Providence getting geared up for the nine [AHL] games left, so it's almost like a quarter of a college year. I had to refocus and say, 'I'm still playing a lot of hockey here, some big-time-meaningful hockey.'"

Because this is Boston's first trip to the Stanley Cup playoffs in three seasons, there's plenty of focus on McAvoy as his career begins at an important time for the Bruins.

"He was awesome," Bruins center Patrice Bergeron said of McAvoy's first two games. "He played well and he wants the puck. He wants to make plays. He's got great speed and great instinct, especially for his age. I was really impressed with him."

With the series tied at 1-1, the Senators want at least a split in the next two games in Boston. Ottawa will attempt to take advantage of the Bruins' injuries. So, how do you exploit a rookie defenseman who has played only two NHL games?

"He sure isn't playing like that. He's a heck of a player," said veteran Senators winger Clarke MacArthur. "He's got patience, and he's definitely been a positive for them. I don't know if you can really exploit him. He skates well. He moves the puck well and, obviously, you just want to keep pressuring him, and pressure all their D and make them make quick plays and hope you can get turnovers off that."

Bruins captain Zdeno Chara has served as a mentor for plenty of young defensemen in the past, but there's something different about McAvoy. It's as though his youth and energy is helping the team more than the team is helping him adjust to the NHL.

"He's really, really steady," Chara said. "He has really stepped up and handled the situation really well. It's obviously a good sign for the future, knowing that he's able to make those adjustments and take the workload, whether it's mental or physical."

McAvoy joined a select group class of American-born players who are having an immediate impact this season. Toronto Maple Leafs center Auston Matthews, Columbus Blue Jackets defenseman Zach Werenski, Calgary Flames winger Matthew Tkachuk and McAvoy were all members of the U.S. national development team roster and still remain close friends.

"It's special to go through it with those guys," McAvoy said. "They've had tremendous years and they got the jump on me. But to see their success and how good they've been doing, it's really cool. We all played together once upon a time, but those friendships have stayed constant and it's really nice to have those guys."

Had it not been for the Bruins' injuries, McAvoy would be preparing for the Calder Cup playoffs with Providence. He's made quite an impression already, and if he keeps it up, it's likely he won't be riding a bus in the minors ever again. He's in the big time to stay.