WASHINGTON — Until a week ago, Braden Holtby’s only NHL playoff experience came from watching games on TV with his buddies.

Still, the 22-year-old goalie for the Washington Capitals thinks like a veteran. When Holtby was so-so in Washington’s Game 3 loss in its firstround series against the reigning Stanley Cup champion Boston Bruins, he didn’t let it bother him. And when the kid gave up a tying goal through his legs in Game 4, he shook that off, too.

The postseason rookie was superb before and after that one blip Thursday night, finishing with 44 saves, and Alexander Semin scored the go-ahead goal, leading the seventh-seeded Capitals to a 2- 1 victory over the secondseeded Bruins that tied the Eastern Conference series at two games apiece.

The Canadian is 16 years younger than Bruins goalie Tim Thomas, who earned last season’s Conn Smythe and Vezina trophies, and is playing in his first NHL postseason because of injuries to Washington’s top two goalies, Tomas Vokoun and Michal Neuvirth.

And the kid has looked like a grizzled veteran for all but Game 3. He stopped 72 of 74 shots in Games 1 and 2, then was terrific again in Game 4. Over the span of about a minute early in the second period,

Holtby made three reflex saves to thwart Bruins chances — and allow the Capitals to win despite playing without their top playmaker, suspended center Nicklas Backstrom.

He was lost for one game after a cross-check to Rich Peverley’s face at the end of Game 3 on Monday drew a match penalty.

Semin put Washington ahead for good by zipping in a wrister from the left circle with 1:17 left in the second on a power-play goal, his second score of the series, which shifts back to Boston for Game 5 on Saturday. Game 6 will be in Washington on Sunday.

Good as Holtby was, Bruins coach Claude Julien was disappointed in his team’s work near the crease.

“That’s the reason we didn’t win tonight. … A lot of loose picks around the net that they cleared and we didn’t get to. The net-front presence has to be better. Not just screening, but also finding those loose pucks. And they’re finding them better than we are,” Julien said. “There’s probably not a good enough commitment in that area right now and until we get that, we’re going to be struggling to score goals.”

Washington was 25-0-1 during the regular season when leading after two periods, and Holtby continued that trend, inspiring repeated chants of “Holt-bee! Holt-bee!” from the red-wearing spectators. After things got rowdy in Game 3, the Capitals did it with discipline Thursday: The hosts were called for only one penalty.

It’s been a tight series all the way, with neither team leading by more than one goal at any moment.

Washington wasn’t called for a penalty until there were just under 10 minutes left in the third period, when forward Mike Knuble — playing because Backstrom was out — was sent off for holding. But the Capitals killed that off without allowing any shots, making the Bruins’ power play 0 for 12 this series.

There was all sorts of verbal jousting during the series’ off days, Tuesday and Wednesday. Hunter — himself no stranger to mixing things up during his playing days — accused Boston of targeting the head of Backstrom, who missed 40 games during the regular season because of a concussion. Julien said that charge was “ridiculous” and “ludicrous.”

After the nastiness in Game 3, the teams returned to the quiet, low-scoring ways of the Games 1 and 2.

“That’s a big game for us, but it’s far from easy from now on,” Holtby said. “It’s a best-of-three now.”

Notes — Capitals captain Alex Ovechkin played fewer than two minutes in the final period, but it wasn’t clear why. … The NHL said after the game that crowd noise resulted in the clock starting 5.3 seconds late after a faceoff in the closing seconds — and so a goal scored with 5.3 seconds or fewer left on the clock would have been disallowed. … Holtby’s save total was the highest for a Capitals goalie all season. … The Capitals blocked 26 shots, 10 more than the Bruins did. … The Bruins outshot the Capitals 14-3 in the first period, and 45-21 for the game. … Boston had won six consecutive road games.