BUFFALO —  The early returns for Rick Nash might have been okay, but the Boston Bruins are staring adversity in the face for the first time since November.

Though they had their chances against the lowly Sabers, the Bruins fell again in another head-scratching performance in a 4-1 setback at KeyBank Center on Sunday. Here is what we learned as the B’s have dropped back-to-back games in regulation for the first time since their four-game skid before Thanksgiving.

Nash creates chances in his debut

Nash certainly had the adrenaline going after arriving from New York earlier in the day. He also had a little bit of an advantage compared to his new teammates in their second game of a back to back.

In his first game since Feb. 18, the 33-year-old fired a game-high five shots on goal and was buzzing around the net during his 17:27 of ice time.

All while adjusting to new linemates — David Krejci and Jake DeBrusk — and new surroundings on the fly.

“It’s still going to take awhile to get in sync with everything that’s been going on,” Nash assessed. “It’s tough when you played a system for so long to mentally turn it over and totally switch neutral zone, forecheck and you know, D-zone [and] O-zone. It’s going to take awhile to adjust.”

Nash’s best chance came toward the end of the second period — in the Bruins best shift of the night — when he hit the post. The missed opportunity cost the Black and Gold a chance to change the momentum and pull within one at 3-2, but that doesn’t discount an otherwise solid night for Nash and an unproductive night for the rest of the team.

The Bruins could still use a defensive upgrade

The Bruins defense has made significant strides under Bruce Cassidy, but things are starting to crack on the back end.

Brandon Carlo is going through one of the worst slumps of his two-year tenure. He was a healthy scratch for the first time in his career less than 24 hours a rough outing the night before in Toronto. Kevan Miller and Adam McQuaid, while serviceable stay-at-home options, aren’t minutes eaters. Torey Krug isn’t producing on the power play (more on that below) and Matt Grzelcyk is still adjusting to his role as a full-time NHLer.

Zdeno Chara and Charlie McAvoy are a viable top pairing, but a top-four defenseman is another area Don Sweeney needs to address before 3 p.m. on Monday. Those chances of a back-end upgrade are unlikely following the Nash deal, but, as has been the case with the NHL’s trade deadline period, stranger things have happened.

Patrice Bergeron is getting banged up

The Hub of Hockey breathed a sigh of relief when Bergeron laced up the skates a night after leaving the Air Canada Centre in a walking boot. But the Hart Trophy candidate had another rough night in the bumps and bruises department after taking a high stick to the face in the first period.

A visibly frustrated Bergeron slammed his stick while going down the tunnel for repairs after that high stick, but did return toward the end of the opening stanza.

Going up against other team’s top lines on a nightly basis is no easy task, but Bergeron has made it look easy throughout his career thanks to his two-way prowess. It can take a toll, however, as exemplified by this weekend’s slate.

“In a sense, I’d like to stay away from those type of plays,” Bergeron said, “but it’s part of the game I guess.”

The Bruins would also like Bergeron to stay away from getting nicked up. After all, the four-time Selke Winner is the last guy they can afford to lose for a significant amount of time.

Special teams aren’t so special of late

The Bruins have been one of the better even strength squads all season long. Their special teams provided a good complimentary presence to their five-on-five play.

The Bruins power play, however, took a dive during their five-game road trip with and carry an 0-for-16 skid back home. Their penalty kill hasn’t fared much better in their recent set of back-to-backs as the B’s went 5-for-8 shorthanded in Toronto and Buffalo.

Though they did go 4-for-5 on the PK, the Bruins allowed two untimely goals to Benoit Pouliot (at 14:26 of the first) and Marco Scandella (at 3:22 of the third) shortly after killing off a pair of penalties.

“Well our power play is clearly in a funk, We’re not executing at the level that we need to and our shot selection can be better, especially on net,” Cassidy said. “PK has [to be] better as well. I think there were a couple of situations where goals were scored with guys coming out of the box and some of that is just our clears.

“I wish I had a great technical answer for you, but right now it’s costing us.”

Special teams were just one part of a costly weekend for the Black and Gold as they drop to third in the Atlantic Division and lose ground on the Maple Leafs and Lightning.