Going into the locker room at the first intermission, the Washington Capitals had no goals but all the momentum.

Three successful penalty kills kept the Philadelphia Flyers off the scoreboard, and the Capitals knew they'd get their chance.

When that happened, John Carlson scored on the power play and the Capitals locked down defensively to shut out the Flyers 2-0 Thursday night in Game 1 of their first-round playoff series.

In a special-teams showcase, Washington leaned on its trademark penalty killing and the goaltending of Braden Holtby to take the lead in the series.

Holtby stopped all 19 shots he faced for his third career shutout in the Stanley Cup playoffs.

"He's been great all year — he's been standing on his head, winning us games and stealing us games," said Jay Beagle, who scored the Capitals' second goal. "With a bunch of (penalty kills), you have to rely on the goaltender quite a bit. He obviously stood on his head again tonight. Those PKs gave us momentum."

The Capitals went 4 for 4 on the penalty kill and frustrated the Flyers, who got only eight shots on net after the first period and lost second-line center Sean Couturier to an upper-body injury midway through the second. Couturier appeared to injure his left arm or shoulder on a hit by Alex Ovechkin and didn't return.

Couturier's status for Game 2 in Washington on Saturday is uncertain. The team said he'd be evaluated Friday.

"All I know is we had to go without him for the rest of the game tonight," Philadelphia coach Dave Hakstol said. "I won't go any further than that."

Couturier's absence could be crushing for the Flyers, especially after they missed several opportunities to score on the power play. The Capitals' penalty kill, which ranked second in the NHL during the regular season, was up to the task early and often.

"If they score there, it's a totally different game," said center Nicklas Backstrom, who assisted on Carlson's power-play goal. "We were staying aggressive and we didn't allow them too much."

Coach Barry Trotz said prior to the game that special teams "can give you momentum or they can take some momentum away from you," and that came true. After his team killed off a fourth penalty in the second period, it got two power plays and started to take over.

Just 19 seconds after Flyers defenseman Brandon Manning went to the box for sending the puck over the glass, Carlson's shot from the point deflected off penalty killer Chris Vandevelde and bounced in past Steve Mason at 16:21 of the second.

Mason was phenomenal in stopping 29 of the 31 shots he faced, but what Backstrom called a "weird shot" from Carlson turned out to be the game-winner.

"When you get a good bounce like that, it's nice," Carlson said. "It's a pick-me-up to start us off."

Carlson's goal was an emotional boost, but the Capitals' methodical defensive play was already well under way. They held the Flyers to a total of eight shots in the final two periods.

"They pressured," Flyers defenseman Mark Streit said. "We've just got to move the puck and keep it simple as much as possible, get pucks to the net and have traffic there. It's easier said than done. They did a pretty good job. We've just got do better."

The Capitals can be better, too, now that they've shaken out whatever rust was left from several months of not playing meaningful games.

For all the talk about flipping a switch for the playoffs, the Presidents' Trophy winners looked playoff ready right away, which could be a bad sign for the Flyers and the rest of the Eastern Conference.

"We didn't have to fake it tonight," defenseman Matt Niskanen said. "We had good focus, good intensity. Really strong effort from a lot of guys and most of the team. I thought we knew exactly how we wanted to play, how we wanted the game to go and we had really good execution."

NOTES: Capitals F T.J. Oshie was in the lineup after leaving practice Wednesday with an undisclosed injury. ... Fans at Verizon Center observed a moment of silence for Flyers owner Ed Snider, who died Monday at the age of 83 after a two-year battle with bladder cancer. Snider was a Washington native. The Flyers wore a patch with Snider's initials, "EMS."