Mason Lohrei scored once and added an assist and the Boston Bruins used a three-goal second period to claim a 5-1 victory over the Florida Panthers in Sunrise, Fla., on Monday in the opener of an Eastern Conference semifinal series.

Morgan Geekie, Brandon Carlo, Justin Brazeau and Jake DeBrusk also scored for the Bruins, who reached the second round of the Stanley Cup playoffs thanks to Saturday’s win over the Toronto Maple Leafs in Game 7 of a first-round series.

Boston goaltender Jeremy Swayman made 38 saves, and Pavel Zacha collected two assists. Swayman has surrendered two goals or fewer in all seven games he has played in the postseason.

Matthew Tkachuk scored for the Panthers, who racked up 110 points in the regular season and finished atop the Atlantic Divisions standings, one point ahead of the Bruins. Florida needed only five games to beat the Tampa Bay Lightning in the opening round of the playoffs.

Panthers goalie Sergei Bobrovsky stopped 24 shots.

Game 2 of the best-of-seven series will be Wednesday in Sunrise.

The Bruins have won all five meetings between the teams in 2023-24 (regular season and postseason) after Florida knocked them out of last year’s playoffs in the first round.

Only 67 seconds after Boston fell behind 1-0, Geekie tied the clash with his third goal of the playoffs at 12:52 of the second period. A Florida turnover resulted in a scramble at the net, and Geekie pounced on the loose puck before sending it past Bobrovsky.

Lohrei’s first career playoff marker came at 16:17 of the middle frame, and it served as the go-ahead goal.

Carlo, whose wife delivered a baby boy earlier Monday, made it 3-1 with 21 seconds remaining in the second. Carlo joined a rush and found the mark from the right circle to net his second goal of the playoffs.

Brazeau added his first career playoff tally 7:13 into the third period by converting a backhanded deke on a breakaway, and DeBrusk added an empty-net goal to round out the scoring.

After a goalless opening period, Tkachuk broke through at 11:45 of the middle frame. Taking advantage of a Boston turnover, Tkachuk gained the puck in the high slot and used a screen to record his fourth goal of the postseason.