The question with your Boston Bruins these days is not if disaster will strike, but when.

The B’s lost a lead for the fourth time in five games on Thursday at the Garden, and for the second time in that span, blew a three-goal lead.

But through it all, the B’s managed to bag the rarest of all birds – a regulation win – thanks to a late Mason Lohrei power-play goal that lifted the B’s to a 5-4 victory over the Vegas Golden Knights.

After Lohrei’s goal, they needed a penalty kill and a couple of huge Jeremy Swayman saves with the Vegas goalie pulled but they white-knuckled the jalopy home.

Morgan Geekie notched his first career hat trick to lead the B’s offensively.

In the first, the Bruins enjoyed their best period since perhaps the win in Philadelphia in the last game before the All-Star break, taking a 3-0 lead on three goals in 80 seconds.

The Knights we playing without their two star forwards, Jack Eichel, who is nearing a return form a knee injury, and Mark Stone, who is reportedly out for the rest of the regular season and perhaps longer.

Coach Jim Montgomery loaded his top line with Brad Marchand, Charlie Coyle and David Pastrnak and they, along with Charlie McAvoy, contributed to pinning the Knights’ ears back in their own zone for most of the period.

But the scoring was done primarily by the bottom six.

It started at 14:34 when Geekie scored the first of his three goals. In the defensive zone, Geekie got a piece of Jonathan Marchessault’s right point shot and it went to Trent Frederic in the high slot. Frederic sent a soft lead pass to spring Geekie for a clean breakaway and he beat Adin Hill with a crisp wrist shot past the glove.

The fourth line doubled the lead on the next shift. Jakub Lauko, returning to the lineup after being scratched in three of the previous four games, chased down a puck behind the Vegas net and made a pretty blind pass out to Jesper Boqvist in the high slot and Boqvist beat Hill with a nicely placed wrister for his fourth of the year.

Finally, Geekie scored his second of the game at 15:04 during a line change. With Danton Heinen on the middle ice net drive, Pastrnak made a nice feed cross-ice feed to Geekie on the left wing and he ripped a shot that the flailing Hill had little chance to stop.

The B’s outshot the Knights, 16-8, in the first and it didn’t seem that close.

Vegas may have been shorthanded but, as champions tend to do, they pushed back in the second period, getting on the board at 1:48 with some great hand-eye coordination from Paul Cotter. From above the right circle, Nicolas Roy sent a high pop-up of a pass that Cotter batted home on Jeremy Swayman’s shortside.

The B’s did not react well.

Vegas kept up the pressure and pulled to within a goal at 6:47 when the top line and defense corps allowed no fewer than four good shots. The first one from Marchessault produced a big rebound for Alex Pietrangelo, who had not one, not two by three chances to put it home and he did.

The first signs of life the B’s showed came after Brandon Carlo took an ill-advised roughing penalty. On the kill, the Heinen could not convert a breakaway and Coyle could not get his pass through Pietrangelo on a 2-on-1 with Pavel Zacha.

That gave the B’s a little momentum and at 16:32, Geekie completed the hat trick. He won an offensive zone faceoff and made his way to the net. From there, he was able to get his stick on Pastrnak’s shot to deflect it past Hill for a 4-2 lead.

But the Knights pushed back when the B’s kicked the puck around in their own end. Chandler Stephenson beat Mason Lohrei to a loose puck behind the net and sent a nice pass out front to Michael Amadio, who scored to get Vegas back to within a goal with 2:14 left in the period.

The Knights had a great chance to even the game late in the period when they had a 3-on-1 but Carlo was able to thwart and send the B’s into the second intermission with aa very precarious 4-3 lead.

And that slim advantage finally evaporated at 5:01 of the third period when the B’s got their first power play and it blew up in their face. Pastrnak couldn’t control a puck at the blue and Stephenson took off on a breakaway, roofing it over Swayman for the equalizer.

But with 4:37 left in regulation, Lohrei gave the B’s a 5-4 lead on the power play, ripping a one-timer off a Kevin Shattenkirk pass that beat Hill through the pads from the right half wall.

It wasn’t over, though. Matt Grzelcyk was called for holding the stick with 2:59 left in the third.