The Boston Bruins had a December – and January – to remember. February began even better.

Four consecutive regulation wins had the Black and Gold knocking on the door of the President’s Trophy as the best team in the NHL coming into Saturday night. Wednesday’s win was arguably the Bruins’ statement of the season thus far, with a second road game in 24 hours against the Rangers; after falling behind, 1-0, Boston stormed back with six unanswered goals for a 6-1 triumph.

The B’s returned home on Saturday evening expecting a proverbial ‘gimme game’ against the lowly Buffalo Sabres. Instead, they had a night to forget.

Here’s what we learned as Boston spotted Buffalo three goals on turnovers and two former Bruins led the way to a 4-2 Sabres win.

Porous “D” leads to second-period giveaways

The Bruins’ defense unraveled itself to Buffalo’s benefit during in the middle 20.

“I just thought we were cute tonight,” Bruce Cassidy said postgame. “You can accept not executing [on] certain nights; you can accept the puck not going in. But…giving them the free chances the other way, that’s just not who we are.”

After a scoreless first, David Pastrnak coughed up the puck, put his seat on the ice, and caused a turnover that sent the Sabres’ Evander Kane in on goal alone from center ice at 7:42 of the second period. Tuukka Rask did not prevail when Kane whistled one home for the 1-0 lead.

Later, at 13:44, Adam McQuaid blocked a shot off his chest and onto the stick of Buffalo center Scott Wilson, who also sent a 10-footer past an unflinching Rask to paydirt for a two-goal lead.

With one minute left, McQuaid’s second gaffe sent Buffalo into a 2-on-1 that ended with former Bruin — and eventual No. 1 star of the game — Benoit Pouliot firing the Sabres into a 3-1 lead.

“We’ve won our share; we’ve learned how to play in those games,” Cassidy said. “It seems like we weren’t going to be respectful of that, and the odd-man rushes, eventually they got us.”

Jake DeBrusk’s pass at 14:39 in the third to a dashing Ryan Spooner, who deflected a slot shot past former Bruins backup Chad Johnson, kept the home team close with Torey Krug also assisting. Spooner’s goal marked six points in his last seven games.

Too little too late to save Rask’s point streak

A Patrice Bergeron shot from the top of the right dot, deflected top shelf by David Backes, cut the deficit to 3-2 at 19:01 in the final frame. The last-minute comeback attempt was short-lived as Rasmus Ristolainen sent a 175-foot shot into an empty Bruins cage 30 seconds later, and the two points went Buffalo’s way.

Thus ended Rask’s career-best point streak of 21 games at 19-0-2. It was the fourth-longest point streak by a goaltender in team history and is the longest since Pete Peeters’ 31-game stretch in 1982-83 at 26-0-5.

“[The puck’s] got to get to the net with traffic, and we just didn’t do enough of that to earn our goals,” Cassidy commented. “It’s ironic we do it with the goalie out late. Too little, too late, but we need a lot more of that early on. I think Tuukka made some good saves on them, too. Could have been a lot worse.”

“Not the way we wanted to play, but those games happen,” Rask added. “Start a new [streak], I guess.”

Plusses get subtracted

How good is Boston’s total team offense and defense? The glaring standout stat is the individual plus-minus. Zdeno Chara at plus-29; Bergeron plus-26; Brad Marchand plus-26; Charlie McAvoy plus-21; and Matt Grzelcyk’s plus-18 lead a starting roster on which every single player is producing on the even or plus side.

Those numbers took a hit Saturday, with a team total of minus-10; Bergeron, Marchand and Pastrnak each notched a minus-2.

“A lot of mental mistakes, if you want to put it that way,” Bergeron assessed. “And they [the Sabres] were coming back at us, and you saw a lot of two-on-ones and breakaways and stuff you don’t want to see.”

Bergeron, Cassidy, and the gang will be hoping to see something better against the New Jersey Devils Sunday night.