They had the momentum heading into their first road trip of the season, but the Boston Bruins couldn’t keep the upward trend going in stop No. 1 of their four-game road trip in Calgary.

The Bruins didn’t play all that poorly, but couldn’t capitalize on their key opportunities. The Flames, meanwhile, got timely scoring from their skilled players and key saves from goaltender Mike Smith in front of their home crowd.

Here is what we learned as the Flames extinguished the Bruins’ four-game winning streak with a highly convincing 5-2 victory Wednesday night.

Tuukka Rask had an up and down night

The mere mention of Rask brings quite the dialogue between his defenders and detractors. Both had a reason to argue their cases on this night.

Already trailing 1-0, a juicy rebound that led to Johnny Gaudreau’s 100th career goal and a botched glove save on Juuso Valimaki’s NHL tally 48 seconds apart put the Bruins in a tough spot late in the first period. Rask stayed in and bounced back with some timely saves in the second and third periods, including a pad stop on Gaudreau’s third period breakaway to keep his team within two at 4-2.

Rask was far from perfect and fought the puck more often than not. But he battled on for 60 minutes and kept his team afloat at certain points, while also keeping Jaroslav Halak rested for his next start Thursday night in Edmonton.

Alas, Rask’s early roller-coaster season rides on.

Bruins power play left powerless

They had a powerful four-game run, but the Bruins power play generated few chances against the opportunistic Flames.

The Bruins power play only mustered two shots on goal in four attempts. No chance was more frustrating than a 5-on-3 opportunity for 58 seconds to start the third period.

With two of the Flames top penalty killers in the box in Mark Giordano and Mikael Backlund, the Bruins failed to fire a single shot on goal to open the final stanza and missed a chance to shift momentum to their side. Instead, Patrice Bergeron and company faced an uphill climb with their two-goal deficit.

Head coach Bruce Cassidy oversaw a power play that entered Wednesday’s contest with a 40 percent success rate. The rare off night dropped the Bruins power play percentage back to 31.3 percent.

Offside challenges are still head-scratching

Fresh off notching his third career hat trick against the Red Wings, David Pastrnak thought he had his fourth goal in two games late in the first period when he fired a shot from the faceoff dot past Smith to cut the Flames lead to two at 3-1. One problem, his fellow linemate Bergeron skated over the blue line before John Moore entered the attacking zone.

The fact that a judgment call is subject to review is mind-boggling, especially since it didn’t directly affect the outcome. It’s clear Bergeron jumped offside, but the play happened several seconds before what would have been Pastrnak’s eighth of the season.

Imagine if baseball managers were able to challenge balls and strikes. If that were the case Game 4 of the Red Sox-Astros ALCS series would still be playing.

Some decisions should be left to the officials’ discretion. In this instance, let the on-ice linesmen do their job. If they miss an offside or two, so be it.