David Pastrnak and Patrice Bergeron celebrate after a 5-2 victory over the New York Islanders in Game 1 of the East Division finals Saturday night in Boston. Elise Amendola/Associated Press

David Pastrnak got his second career playoff hat trick, David Krejci had four assists and the Boston Bruins beat the New York Islanders 5-2 on Saturday night in the opening game of their second-round playoff series.

Charlie McAvoy and Taylor Hall also scored, and Patrice Bergeron had a pair of assists for the Bruins, who will host Game 2 on Monday night.

Tuukka Rask finished with 20 saves as the Bruins kept most of the action at the other end of the ice, outshooting the Islanders 40-22.

Rask didn’t allow anything past him after Adam Pelech’s goal for the Islanders 12:34 into the second period tied it at 2. It was one of only four shots in the period for the Islanders, who were playing before a rowdy crowd of fans who packed TD Garden for the first time in more than a year.

Anthony Beauvillier also scored for the Islanders, Jordan Eberle had two assists and Ilya Sorokin finished with 35 saves, keeping New York in it through the first 40 minutes despite the onslaught of shots from the Bruins.

Sorokin stopped Pastrnak twice on one-timers from in close in the first period, but he converted the rebound of a Krejci shot to tie the game, the but the Bruins ahead in the second period with his second goal.

Pastrnak, whose first postseason hat trick came three years ago in Game 2 of the opening round against Toronto, scored his third goal by weaving through the Islanders zone after a steal and ripping a wrist shot past Sorokin 14:10 into the third period.

The hats began flying from all levels of of the arena, which got loud enough to shake over the few minutes it took to clear the ice as elated Boston fans celebrated being back inside the arena and another victory by the Bruins.

Pastrnak’s goal and an empty-netter by Hall triggered several anti-New York chants and a few rounds of “We Want The Cup!”

With the game tied at 2, the Bruins regained the lead for good 6:20 into the third on a slap shot by McAvoy for his first goal of the playoffs. Boston had just successfully killed a penalty for having too many men on the ice and was in control the rest of the game.

The Islanders had been able to match the Bruins through the first two periods despite the wide offensive disparity.

Sorokin still stopped 17 of Boston’s 18 shots in the opening 20 minutes, while Rask faced only eight at the other end. The second period was more of the same, with Boston holding a 12-4 shots advantage and both teams scoring one goal.

The Islanders led 1-0 after Beauvillier scored 11:48 into the first on a tip. But New York took a late penalty when Andy Greene was called for high sticking with 32.3 seconds left in the first, which was more than enough time for Boston’s “Perfection Line” to tie it before the end of the period.

Bergeron won the faceoff after the whistle and got the puck to Krejci for a shot that Sorokin stopped, but deflected the rebound to his right. Pastrnak was waiting in the circle and took a moment to corral the puck, then fired a wrister past Sorokin.

Pastrnak’s second was very similar to the first, a rebound kicking off Sorokin’s pad right to Pastrnak for a one-timer 8:52 into the second that put Boston up 2-1.

CANADIENS 3, MAPLE LEAFS 2: Jesperi Kotkaniemi scored at 15:15 of overtime and Montreal won at home to force Game 7 in the first-round series.

Corey Perry and Tyler Toffoli also scored and Carey Price made 41 saves in front of the first Canadian hockey crowd since the start of the pandemic.

With his team outshot 13-2 in the extra period and struggling to generate anything, Kotkaniemi ripped a shot past goalie Jack Campbell’s glove side after Toronto defenseman Travis Dermott turned the puck over to Paul Byron.

Jason Spezza and T.J. Brodie scored for Toronto, beating Price with under 10 minutes to go in regulation to tie it. Campbell stopped 28 shots.

Game 7 is Monday night in Toronto, with the winner moving on to face Winnipeg. Also an overtime winner in Game 5 in Toronto, the Canadiens are looking to come back from a 3-1 series deficit to win for the third time in franchise history.