"It definitely helps my confidence to come in and help the boys win," said Fabbri, who was acquired from the St. Louis Blues in a trade for forward Jacob de la Rose on Wednesday. "That's what I'm going to be trying to do here."
Dylan Larkin and Anthony Mantha scored for Detroit (5-12-1), which ended a four-game losing streak. The Red Wings had gone 1-11-1 since starting the season with three wins in four games.
WATCH: [All Bruins vs. Red Wings highlights]
Bernier, who made 26 saves, was the first Red Wings goalie to have two assists in a game since Jim Rutherford did it on Feb. 18, 1979, in a 6-2 victory against the Pittsburgh Penguins. Tuukka Rask of the Bruins was the last NHL goalie to have two assists in a game, in a 4-1 win at the Winnipeg Jets on Oct. 17, 2016.
"Someone just told me I have seven (career) points now, which I didn't even know," said Bernier, who had never had two assists in a season.
David Krejci and Patrice Bergeron scored for Boston (11-3-2). David Pastrnak's 13-game point streak ended when a scoring change took away an assist on Boston's second goal.
Rask made 28 saves for the Bruins, who have lost two straight after a six-game winning streak.
"We just didn't have enough energy tonight," Krug said. "It showed up late in the second, but we couldn't get over the hump."
Fabbri scored two power-play goals on passes from Tyler Bertuzzi, his junior teammate for three seasons with Guelph of the Ontario Hockey League.
"It was a lot of fun to play with [Bertuzzi] back then, and tonight brought back all of those memories," he said.