Despite their gaudy record and spot atop the Atlantic Division, the Bruins are not a team that can show up to a game a half hour late and steal a win.

They learned that lesson on Thursday night at the Garden, when the previously struggling Buffalo Sabres took it to the B’s for the first half of the game and took home a well-deserved 3-1 victory.

The Sabres, playing without top defenseman Rasmus Dahlin (lower body), scored a pair of goals in the second period and one in the third and that was good enough.

What was more concerning than the defeat was the loss of Charlie McAvoy, who left the game with an apparent head injury in the third period.

In the first period, the Bruins looked like a team that had three days off and needed to shake off the cobwebs. They were outshot by the Sabres 19-6.

It was a scoreless first period, though it briefly looked like the Sabres had taken a lead with 5:18 left in a weird sequence. Newly acquired forward Eric Robinson poked the puck home under Linus Ullmark. It was initially waved off by the official behind the net but, after a conference during the commercial break, the Sabres were awarded the goal.

Then B’s coach Jim Montgomery challenged for goalie interference and the video clearly showed that Kyle Okposo had shoved Ullmark into the net with his stick, allowing Robinson to get at the puck. The goal rightly came off the board, but they couldn’t hold the Sabres at bay with the amount of time they were allowing their visitors in the Boston zone.

Buffalo did get its 1-0 lead early in the second period at 1:18, on a simple play. Dylan Cozens cleanly beat Pavel Zacha in a faceoff at the left circle, drawing it straight back to J.J. Peterka, who seemed to surprise Ullmark with a snap shot over the glove.

The B’s, who were without rookie Matt Poitras (first healthy scratch), needed to find both their legs and hands, but they were hard to locate on this night.

They caught a break when killing a penalty for too many men on the ice. It looked like they might go down two men when Cozens was tripped at the Boston blue line but it was let go. Then a few seconds later, Tage Thompson was called for slashing Zacha’s stick. But the B’s could do nothing with the 4-on-4 or the 1:02 of power play time.

They did start spending a little more time in the Buffalo zone, holding an 11-9 shot advantage in the second. But after Devon Levi stoned Brad Marchand on a glittering chance from the slot, the Sabres took a 2-0 lead. Old friend Connor Clifton jumped down from his right point spot past James van Riemsdyk to win a puck along the half board and feed Thompson, who whistled it past Ullmark at 16:57.

But just 38 seconds later, the B’s finally got one back with 2:25 left in the period, thanks to a fortunate bounce. Marchand drifted up into the right circle and, without much of a play, he fired the puck toward the net. It bounced off Sabre defenseman Erik Johnson and past Levi for Marchand’s 12th of the season and the fifth straight Bruin goal scored by the captain, dating back to his overtime game-winner last Saturday in Toronto.

The B’s pushed hard in the third period with lots off offensive zone time, but the usually porous Sabres played well in front of Levi. Eventually, they busted out on a 2-on-1, with Victor Olofsson taking the shot and snapping it past Ullmark with 8:44 remaining in regulation, ending a period of 10:30 of continuous play.

At that point, it did not look like it was going to be the B’s night, especially after the B’s had lost McAvoy when he was dazed on a reverse hit from Peterka.

The B’s pulled Ullmark with over three minutes left and kept the puck in the Buffalo zone for almost all of it, but couldn’t get another past Levi.