PHILADELPHIA — The Bruins had a pair of goals waved off in the first period, and quickly had their entire night wiped off the board Thursday night in a 5-1 preseason loss to the Flyers at Wells Fargo Center.

Travis Konecny, Jakub Voracek, Brendan Manning, Wayne Simmonds, and Sean Couturier all scored for the Broad Streeters, who built a commanding 4-0 lead by the middle of the second period.

David Krejci scored Boston’s lone goal.

The result, which dropped the Bruins to 4-2-0 in the exhibition season, might have been different had first-period strikes by Anders Bjork and Jake DeBrusk not been struck from the record.

Bjork connected at 10:36, rushing to the net and potting a rebound of a Patrice Bergeron shot. But the 1-0 lead was waved off immediately, on-ice officials ruling that linemate Brad Marchand initiated Bjork’s shot with a hand pass.

Next, only 49 seconds after Konecny supplied the 1-0 lead for Philly, DeBrusk had his goal voided when video review showed he interfered with ex-Yale goalie Alex Lyon.

With only 11 seconds left in the period, Voracek bumped the Philly lead to 2-0, setting the stage for the night’s thorough thrashing.

Tuukka Rask, who allowed four goals on 18 shots across the first 40 minutes, yieled the Boston net to Malcolm Subban to start the third period. Subban turned back five of the six shots he faced.

Unlikely fight

Krejci, rarely involved in fisticuffs, dropped gloves with Nolan Patrick late in the second period after the two jawed back and forth for an extended period in the midst of a 10-man scrum in the Boston end of the ice.

Krejci, who needed most of last season to recover from offseason hip surgery, was the first to throw down. The young Patrick, the No. 2 pick in this past June’s draft, traded a few shots with the Bruins No. 2 center, but neither combatant appeared to inflict any significant damage — no doubt a relief to both benches.

Krejci’s goal was set up by Kenny Agostino only 48 seconds into the third period.

Agostino, who supplanted DeBrusk on the second line, tossed a pass into the right circle that Krejci collected and snapped home short side on Lyon.

Decision time

Coach Bruce Cassidy, who’ll pare down the roster following Saturday’s exhibition wrapup in Chicago, still has decisions to make on the third and fourth lines, and the third defensive pairing.

The third line, a.k.a. grind line, will be anchored by Ryan Spooner, with veteran David Backes on his right wing. Sean Kuraly, naturally a center, is the odds-on favorite to begin the season as the line’s left wing.

“I think we have a pretty good idea who’s in the mix,’’ said Cassidy. “Kuraly, I think, is still in a battle. He’s only been around for one year. We know Spooner is going to be on the team and in the lineup. Same for Backes . . . and [Riley] Nash. So it’s more about fitting the pieces together.’’

Veteran Matt Beleskey, a bit leaner and faster this preseason, also remains in a fight for a spot, along with Frank Vatrano, Tim Schaller, and Noel Acciari — all of whom filled various roles with last season’s varsity.

“So part of the third line is definitely going to be here,’’’ added Cassidy. “It’s just which guy is going to be with them.’’

Assuming Kuraly holds down the No. 3 left-wing spot and Beleskey remains employed on a fourth line with Nash, then it comes down to the rest of the remaining forwards to battle for one open spot. That would include Vatrano, Schaller, Acciari, Danton Heinen, Austin Czarnik, Jakob Forsbacka Karlsson, and free agent pickup Agostino.

Teddy Purcell, in camp on a tryout, also remains a consideration.

But Cassidy sounded reserved about the veteran winger’s chances.

“He knows this . . . he was told up front that he was an insurance policy if some of these younger kids couldn’t play up in the lineup,’’ said the coach. “And then if he kind of knocked our socks off, we might have him and the young guys. He’s played well, but the young guys have played well, too, and we are happy with them. So right now he is competing, but it is tougher for him with these young guys doing well.’’

Overall, Cassidy favors a 22-man roster, with only one extra forward and one extra defenseman to work into practices.

“I found eight defensemen last year to be difficult,’’ noted Cassidy, often with the likes of Joe Morrow and John-Michael Liles going long stretches without game action. “We had times with Morrow and [Colin] Miller both out, and it’s difficult when they are that young. When it was Liles, who knew the drill a little more, it’s a little bit easier. So seven D for me. Two extra forwards is OK . . . but ideally, one [D] and one [F)], you see a lot of teams doing that.’’

Adam McQuaid will make up half of Boston’s No. 3 D pairing, but Cassidy needs to find the fill-in for the injured Torey Krug (broken jaw), McQuaid’s regular partner on the left side. Matt Grzelcyk, Rob O’Gara, and Paul Postma all remain in the mix.

Settling the net

Anton Khudobin, last season’s backup goalie, will get the start Saturday night. Subban most likely again will share the net in AHL Providence with Zane McIntrye.

“Malcolm needs to play,’’ said Cassidy. “Tuukka is going to get the lion’s share of the games. And we don’t have a heavy workload early, so three goalies would not be something we would be looking at. Right now, we are comfortable with Anton.’’

Khudobin, who suffered a minor injury at the start of the week, practiced Thursday morning in Boston, prior to the team flight here early in the afternoon. Subban, if sent to Providence, must clear waivers. However, if a club were to claim him, Subban would have to be left on the acquiring team’s NHL roster — likely minimizing the chance he would be claimed.

Big fan of Bjork

Cassidy remains particularly enamored with Bjork, whose quick acceleration and sustained speed could make him one of the club’s most exciting wingers in years. “Listen, it’s a split-second game,’’ said Cassidy. “He has the foot speed, courage, confidence to do all that. I think that’s why he’s looked good. He’s not getting in his own way. I really believe that with this kid. He has taken the bull by the horns. He’s playing with good players and he is not getting in his own way — he is playing to his strengths and he looks good doing it.’’ . . . The Bruins will work out Friday at Warrior Arena in Brighton and then wrap up their preseason schedule Saturday night in Chicago. The puck goes down for real on Thursday at 7 p.m., with the Nashville Predators in town.