The Bruins had their record-setting victory in their sights on Thursday at the Garden and booted it away.

Going for the franchise best 7-0 start, the B’s coughed up a two-goal lead late in the third period and then Mason McTavish scored at 2:52 of overtime to lose 4-3, suffering their first loss of the season in brutal fashion. They fell to 6-1.

The B’s appeared to be well on their way sealing their seventh win when Patrick Brown took holding penalty with 4:00 left and the Ducks pulled goalie John Gibson for a 6-on-4. The B’s had several chances to clear but failed and with 1:55 left in regulation, Leo Carlsson scored a 6-on-5 goal to cut the Bruin lead to a goal.

The B’s inability to clear the zone continued and Sam Carrick tied the game with 14.7 second left in regulation to make it 3-3.

As we’ve come to expect in the first game back after a long, successful road trip, the Bruins were pretty lifeless in the first period. The Ducks, meanwhile, looked like they were putting a wakeup call to good use. In their win in Columbus on Tuesday, Anaheim coach Greg Cronin benched star forward Trevor Zegras and, in the first period at he Garden, the Ducks were battling for every puck.

While the Ducks, who held a 9-6 shot advantage, had the better of the chances in the first, they took the lead at 15:00 of the first on a fortunate bounce. With Mason McTavish battling for position in the crease with Hampus Lindholm behind goalie Linus Ullmark, Radko Gudas threw the puck toward the net and it deflected home off Lindholm.

B’s coach Jim Montgomery, after a fair amount of debate on the bench, elected to challenge the play for goalie interference but the goal was upheld.

The B’s killed off the resulting penalty, their second of the period, and went into the break down a goal.

The B’s shook off the cobwebs in the second period and stormed to a 3-1 lead.

Rookie Matt Poitras, who came into the game with three goals in two games – including two in Anaheim – was predictably earning more attention. He was high-sticked in the first period on a play that wasn’t penalized. Then early in the second period, he was cross-checked by Jackson Lacomb. That one was called, and the B’s made the Ducks pay as their struggling power play got off the schneid.

After changing on for James van Riemsdyk, Charlie Coyle won a faceoff in the right circle and went to the net. He was at the top of the crease to redirect David Pastrnak’s fanned-on slapper attempt into the wide open net behind John Gibson at 1:41 for his first of the season. The teams were officially even on lucky bounces.

As things got chippy, Coyle and Frank Vatrano received matching crosscheck penalties and the B’s took the lead on the ensuing 4-on-4. Poitras made zig-zags along the left side of the offensive zone and got it up to Charlie McAvoy at the blue line. McAvoy fed Matt Grzelcyk in the right circle and his blast squeaked through Gibson’s pads for Grzelcyk’s first of the year at 3:01.

The B’s came close to extending the lead on a penalty kill when Patrick Brown fed John Beecher with an empty net but the rookie hit the post.

They did get the third goal with 3:20 left in the second. McAvoy rushed the puck through the neutral zone and, once he gained the blue line, dished it to Pastrnak on the left wing. Pastrnak took a shot that handcuffed Gibson and produced a succulent rebound. Pavel Zacha fouled off his swing but Pastrnak was able to swoop in and deposit his sixth of the year into the empty net.