For three full periods of scoreless hockey, the Washington Capitals found themselves heavily outshot and often trapped in their own end, fending off waves of attacks from the defending Stanley Cup champion Boston Bruins and relying on perfection from rookie netminder Braden Holtby. It was a dangerous and unsustainable trend that proved costly when the contest drifted past regulation.

One minute 18 seconds into overtime at TD Garden on Thursday night, Chris Kelly fired a shot past Holtby’s outstretched glove to give Boston a 1-0 win in Game 1 of this Eastern Conference quarterfinal series. Given the number of chances the Bruins manufactured through the first 61 minutes of play, it was a testament to Holtby that they hadn’t cashed in sooner.

For 22-year-old Holtby, the goal — which appeared to have been tipped by Dennis Wideman — was an unfortunate end to a strong 29-save showing in his Stanley Cup playoff debut. He was ultimately outdueled by the reigning Conn Smythe and Vezina Trophy winner Tim Thomas, who was tested far less and finished with 17 stops.

“I think he played a hell of a game,” Capitals captain Alex Ovechkin said of Holtby, whose teammates rushed over in a show of support after Boston captured the victory. “Most of the time he kept us in the game and I think he was nervous, but after the first shot you could see he was calm and he was on his roll.”

Holtby was tougher on himself, but the consensus among his teammates and Coach Dale Hunter was that the youngster had nothing to be displeased with.

“I felt all right,” Holtby said. “Later on in the game I felt like there were some things I needed to be better at. I got a little sloppy with some things and those are the things I’ll need to make improvements on for the next game. But mainly, I wasn’t there for the boys in overtime and I’ll definitely be better for that.”

After months of talking about playoff hockey, the Capitals kicked off the real thing in front of a raucous, hostile crowd and against a rabid Boston roster that introduced itself with glass-rattling hits, followed by more hits, with a few additional hits for good measure.

Holtby appeared to fight the puck at times early on, giving up prime rebounds, but the Saskatchewan native’s confidence grew with each shot he faced.

Weathering the early physical onslaught yielded a power play for Washington when David Krejci received a minor penalty for boarding after crunching Wideman in the corner. The start of the playoffs didn’t offer a magic cure-all to the Capitals’ struggles on the man advantage, though.

Washington went 2 for 24 on the power play to close out the regular season and its opportunity of the playoffs yielded the same woeful results. The Capitals recorded one shot on goal — from 58 feet away — during the two-minute span, which they largely spent chasing Boston’s clearing attempts.

Luckily for the visitors, the Bruins’ power play wouldn’t find success, either, despite four opportunities.

Washington withstood Boston’s man advantage by limiting most of the shots to the outside, and when they did fire the puck it rarely reached Holtby. From the beginning of the contest it was clear the Capitals intended to block as many shots as possible. That was most apparent while they were short-handed, as players dove in front of chances and scrambled to turn into a point blast rather than away from it.

“I thought our killers did a good job,” forward Brooks Laich said. “Going forward in the series, we’re going to have to stay out of the box a little bit more. It leaves our offensive guys on the bench and taxes our other guys.”

That continual effort to not allow shots to find their target helped Washington thwart Jay Beagle ’s double minor for high sticking and an ill-timed delay-of-game infraction by Troy Brouwer, who shot the puck over the glass just two seconds after the previous one expired. All told, the Capitals endured a stretch of six minutes short-handed in which they blocked eight attempts; Boston recorded seven shots on goal in the same span.

The lack of creating substance on the power play didn’t deter the Bruins’ fundamental game plan of hitting anything that moved in an opposing sweater. While there may not be much pre-existing animosity between these two teams, it isn’t taking long to create some.

What started with thunderous checks — including several exchanged by Ovechkin and Dennis Seidenberg — boiled over into tangles after the whistle. With just more than eight minutes gone in the second period, Krejci ran into Holtby after the netminder made a stop. John Carlson came to Holtby’s aid immediately, shoving Krejci away and drawing the rest of the players on the ice into the fracas. Milan Lucic took swings at Nicklas Backstrom, Carlson and Krejci continued to swing at each other and the latter pair found itself with matching roughing minors.

The game remained mired in a scoreless tie through 40 minutes, but it was lopsided elsewhere. Boston had out-shot Washington 26-7 heading into the third frame. After the game, the Capitals focused on the bright side: They stayed in it despite being thoroughly out-chanced and having to kill numerous penalties.

“I think we were happy that we were still in the game,” Backstrom said. “An away game, on the road, it’s good to be tied before the last period.”

Early in the third period, the Capitals came up with their best attempt to foil Thomas on a power play gleaned from a cross-checking call against Boston all-star defenseman Zdeno Chara. Tic-tac-toe passing led to a wicked one-timer, back door from Ovechkin that seemed to have caught the Bruins unaware. But as the puck flew toward the cage, Thomas made a diving split across the goal mouth to the left post, where he stopped the shot.

Regardless of the specifics, the Capitals didn’t want to spend much time dwelling on the single loss. There’s no denying that finding a more consistent offensive presence, both at even strength and by not handcuffing themselves with consecutive penalties, will need to be a priority.

“I’m sure we could have done a lot of things better,” Carlson said. “Overall, I thought we played well, though certainly we do need to score.”