NEW YORK — New York Rangers rookie forward Matt Rempe said that “shock” was the first emotion he felt after scoring the opening goal of their playoff series against the Washington Capitals on Sunday.

“I was like, ‘Oh my gosh.’ It didn’t really kick in, and then you hear the crowd. It was a dream come true. It was unreal,” he said, after the Rangers’ 4-1 victory to take a 1-0 lead in the first-round playoff series.

Rempe’s goal at 4:17 of the second period sparked the Rangers’ offense, as they built a 3-0 lead in a 2:06 span after he scored. But the entire game just added to the cult hero status of the 6-foot-7 rookie, whose energetic fights and big hits endeared him to Rangers fans who loudly chanted his name in Game 1.

“I love them. They were chanting all night and I love them so much,” Rempe said. “I can’t thank them enough.”

One of those fans was his mother, Janice, who was watching her son play for the first time at Madison Square Garden.

“It was really special for her to be there,” he said. “I love her so much. I’m her biggest fan. We went out for dinner last night and walked around. She had never really been to New York, so we were just walking around. I bet she was pretty emotional today, so it was really cool.”

Rempe took his first playoff shift 50 seconds into Game 1, sparking a “REM-PE” chant from the sold-out Madison Square Garden crowd. Just over a minute later, Rempe was in the penalty box, having been called for charging against the Capitals’ Beck Malenstyn. As they would throughout Game 1, the Capitals failed to score on the man advantage, going 0-for-4.

Rempe spent just 26 seconds more on the ice than in the penalty box during the first period, a ratio familiar to Rangers fans who watched his rookie season.

But in the second period, Rempe made a game-changing play not with his physicality, but with his offense.

Rempe carried the puck into the attacking zone, circled behind the net and then tucked a pass from teammate Jimmy Vesey into the Capitals’ net at 4:17 for his first playoff goal and a 1-0 lead for the Rangers.

“I think any game he’s in the lineup, he’s had an effect on the game. He shows up every night for the team and it’s great to see him get that goal,” Vesey said. “It was a big goal in the game obviously, but the look on his face was pretty cool, too.”

That goal shifted the momentum to the Rangers, who built a 3-0 lead over the next 2:06 in the second period on goals from Artemi Panarin and Vesey, on a play that had another Rempe moment.

After Barclay Goodrow won the faceoff, Rempe collided with Malenstyn, knocking him to the ice in the slot. That helped clear the path for Vesey to beat goalie Charlie Lindgren with a long-distance shot that was deflected. Capitals defenseman John Carlson protested to the officials about the play. Replays appeared to show Malenstyn skating into Rempe after the faceoff.

“You’re anticipating a [faceoff] loss, so you’re trying to jump through. And then when [Goodrow] wins it back, I want to get a pick. I don’t really know what happened. Next thing you know, Jimmy scored. So I was just happy Jim scored,” Rempe said.

Rempe ended the night with a goal, a plus-2 rating, two penalty minutes and two shots on goal in 8:33 of ice time. When the Capitals tried to engage with him physically, he’d smile and skate away.

It has been a learning experience for Rempe from his NHL debut in the Rangers’ MetLife Stadium Series win over the Islanders on Feb. 18 to earning a place in the lineup for Game 1 of the playoffs. After five fights in his first six NHL games and a four-game suspension in March for elbowing New Jersey defenseman Jonas Siegenthaler, Rempe had only one fight in his last seven regular-season games.

After Game 1, Rempe said he was proud to have made an impact in the postseason for the Rangers.

“I know my game. I know I can skate well and be physical. I think I can be a real pain to play against down low, protecting pucks and going to the net,” he said. “I think I’m built for the playoffs. I think that that’s where you want to play and I was happy how tonight went.”

Rangers coach Peter Laviolette said that in his 22 seasons behind the bench in the NHL, he couldn’t recall another first-year player like Rempe.

“I can’t think of a player that’s come in and had that kind of impact on a team, on a fan base and on the city,” he said. “If you watch him, he just smiles. He’s just happy. Loves being here, loves to play the game. He’s been great.”

Game 2 is Tuesday night at Madison Square Garden.