Like most 19-year-olds, David Pastrnak is lively enough to make it through a day without assistance from caffeine.

But in Saturday’s second period, had he wanted to, Pastrnak could have sipped from a cup of coffee and chased it with a pastry while waiting for David Krejci to get him the puck.

“I had a little break there in front of the net, waiting for Krech to get to the shooting position,’’ Pastrnak said after the Bruins’ 3-1 win over the Islanders at TD Garden. “Then he just made a great pass. I jumped to the back door and he found me. Really nice play by him. For me, I will say it was really easy to shoot the puck at the net.’’

Krejci did the heavy lifting on Pastrnak’s first of two goals. The center circled around the offensive zone with former teammate Johnny Boychuk in full pursuit. Krejci’s slow-motion loop did two things. First, it pulled Boychuk, who is good at the muscle stuff in front of the net, out of his down-low office. Second, Krejci’s lap put Frans Nielsen into a puck-watching trance. Pastrnak was Nielsen’s man.

So as his skilled center looked for something to happen, Pastrnak did the right thing. He gained position in front of the net, put his stick on the ice, and waited for the puck. Krejci, as he usually does, knew what to do. With 8.9 seconds remaining in the period, Pastrnak tucked the game-winning goal behind Thomas Greiss to crack the Islanders.

With injuries, rust, and a dip in confidence behind him, Pastrnak has regained his status as an offensive difference-maker. In the third period, after taking a long-distance pass off the wall from Loui Eriksson, Pastrnak had a bad-angle look on Greiss. Pastrnak was aiming for Greiss’s blocker. The right wing misfired and the puck went glove side instead. The puck still went in at 17:26 to give the Bruins a 3-1 lead. Pastrnak has four goals in his last four games.

“It definitely helps for my confidence,’’ Pastrnak said. “I’m trying to focus on getting better on the little stuff. I’m young. I’m learning. I’m trying to learn from guys like Krech, [Patrice Bergeron], Loui, and guys with a bunch of experience. The more experience I can have, the better player I can be.’’

Pastrnak and his second-line mates started the game slowly. But they found their legs and carried the offense. The first line went scoreless while being matched against Josh Bailey, John Tavares, and Kyle Okposo. Its lack of production did not hurt the Bruins because Pastrnak, Krejci, and Eriksson (one goal, two assists) led the offensive charge.

Pastrnak is a dynamic offensive player. He does not need much time to accelerate from zero to 60 m.p.h. Pucks slingshot off Pastrnak’s whippy stick so violently that goalies do not like seeing him in dangerous areas. Pastrnak is sneaky good at snapping sharp-angle passes through seams to his teammates.

It hasn’t been automatic, however, for coach Claude Julien to deploy Pastrnak as a chance-producing weapon. Pastrnak remains a work in progress, like most players his age. In 15:51 of ice time on Saturday, he was tagged with six giveaways, which is not always a reliable statistic. That the number was so high, however, indicated that Pastrnak was not exactly diligent with the puck.

This is not a new thing. Against Florida on Monday, the teenager’s unreliable defensive play prompted Julien to tighten the leash. Pastrnak played only 9:33, his lightest workload since Jan. 19 against Montreal, when he played just 7:05.

“There’s definitely areas where you look at his game, such as tonight, he was really good for us,’’ said Julien. “We all see, people who know the game, will see also those areas he has to improve. He has to get stronger on the puck and not turn them over as much as he does. It’s going to happen in a game. It’s about playing the clock as well and looking where you are. If you’re up by one in the last few minutes, you can’t afford big turnovers. It’s about making the right decisions. It’s about playing the game the proper way at the right time. To me, he’s learning that part of it. Tonight, I thought he was better than he had been in some other nights where I had to some of his ice time away.’’

Earlier this season, when Pastrnak’s carelessness with the puck and passivity in hostile situations flared up, the Bruins were in trouble. Pastrnak’s shortcomings coincided with the flickering play of fellow right wings Brett Connolly and Jimmy Hayes. When Julien distributed Pastrnak’s shifts elsewhere, the coach wasn’t getting better performance from his alternatives.

It’s different now. The addition of Lee Stempniak has not only improved the first line but helped to stabilize the right side. Connolly is better on the fourth line than on the first. Pastrnak is serving as a dangerous offensive presence more frequently. Hayes is stuck in one of his troughs (0-0—0 in the last seven games), but the Bruins are surviving the No. 3 right wing’s disappearance because the others are pulling their weight.

Pastrnak is hot. So are the Bruins. The two go hand in hand.

Fluto Shinzawa can be reached at fshinzawa@globe.com. Follow him on Twitter @GlobeFluto.