PHILADELPHIA -- Once it came down to a shootout, this was no contest.
Thomas finally allowed a shootout goal after going 9 for 9, but he stopped Wayne Simmonds to end it.
Meanwhile, Bryzgalov has allowed goals on all five shots he's faced in shootouts this season.
"As a goalie, I would prefer to go to shootout at 1-1 or 2-2," Thomas said. "We need to improve. We played some real good hockey a majority of the year. We've found a way to get points. It's nice to win, but we want to do it the right way."
The Northeast Division-leading Bruins haven't lost in regulation in Philadelphia since March 10, 2007, going 9-0-1. The defending Stanley Cup champions are tied with the New York Rangers for first place in the Eastern Conference.
Scott Hartnell scored a natural hat trick in the second period and Max Talbot had two goals for Philadelphia.
Philadelphia's Matt Read missed the net on the first shot in the shootout. Krejci then scored for the Bruins. Claude Giroux answered for Philadelphia, becoming the first person to score on Thomas in three shootouts this season.
After Seguin beat a sprawling Bryzgalov, Thomas stuffed Simmonds.
"Our whole team could have been better," Bruins coach Claude Julien said. "[Thomas] was bombarded with shots. There was a lot of traffic. We battled hard and did what we had to do to win."
The injury-riddled Flyers, already missing captain Chris Pronger for the rest of the season because of a concussion, played without Danny Briere (concussion) and Jaromir Jagr (lower body injury). Both players were injured in Saturday's 4-1 win at New Jersey.
Coach Peter Laviolette was encouraged by the team's performance this weekend without some of its star players.
"It's hard when you lose a game," he said. "Overall, the effort was some of the best I've seen."
Leading 4-3 to start the third, the Flyers failed to become the first team to overcome a two-goal deficit against Boston this season.
Krejci redirected Rich Peverley's shot to tie it at 4 just 1:19 into the third period. Campbell scored the go-ahead goal less than four minutes later when he tapped in Daniel Paille's wraparound shot.
Talbot tied it at 5 when he tipped Matt Carle's slap shot past Thomas during a power play.
These teams have become rivals after meeting in the playoffs the past two seasons. The Bruins won their sixth Stanley Cup last year, sweeping Philadelphia out of the Eastern Conference semifinals in the process. In 2010, the Flyers overcame a 3-0 series deficit and 3-0 deficit in Game 7 and beat Boston in the semis.
"They are a team with a lot of pride," Lucic said. "We expected them to be tough. The Flyers always bring their best. We are two of the top teams in the league. We've played well all season and it's great to get a win."
The shaggy-haired Hartnell, having the best season of his career, scored three straight goals to give the Flyers a 4-3 lead in the second. He leads the team with 25 goals, five shy of his career high set in 2008-09.
Despite his success, Hartnell wasn't selected to play in the All-Star game next week in Ottawa.
"I haven't really thought about it," he said. "It would've been a treat to get picked and get credit for the start of the season. Last couple games have been pretty good. I have plans made already. But if I get the call [to replace someone], I'd be there in a heartbeat."
Hartnell got Philadelphia within 3-2 on a power-play goal a few minutes into the period when he blasted a one-timer while down on one knee.
Hartnell then scored a nifty goal to tie it at 3. He caught a pass from Giroux, dropped the puck, turned around and lifted a shot over defenseman Adam McQuaid that fluttered above Thomas' stick.
Hartnell put the Flyers up 4-3 in the final minute of the period. He lost his stick during the shift, skated over to the bench to grab another one, returned to the circle and ripped another shot past Thomas.
Fans littered the ice with hats to celebrate Hartnell's sixth career three-goal game and first since Dec. 20, 2008. With only 46.5 seconds left in the second, players went back to their lockers and added the extra time to the final period.
Bergeron scored his 15th goal to give the Bruins a 1-0 lead just 50 seconds into the game.
But the Bruins answered with two goals in a span of 3:29 to go up 3-1.
Seguin scored his 18th goal near the midpoint of the first. Lucic then fired a shot from the slot over Bryzgalov's shoulder to put Boston ahead 3-1.
There were two fights and another scuffle during a feisty first period. Tom Sestito, just recalled by the Flyers because of the injuries, dropped the gloves against Lucic early in the game. Later, Boston's Chris Kelly went after Brayden Schenn after the rookie delivered a crushing check on Steven Kampfer. Bryzgalov then got a roughing penalty that precipitated a shoving match.
Players squared off two more times during the game. The Flyers and Bruins are the two most penalized teams in the NHL.
- Bruins D Andrew Ference was suspended three games without pay by the NHL for boarding New York Rangers defenseman Ryan McDonagh during overtime of a 3-2 loss on Saturday. The suspension will cost Ference $36,486.48. "My opinion [on the ruling] I think is best reserved for friends and family," Ference said.
- Shelley surpassed 1,500 career penalty minutes with his fight.
- Briere is out indefinitely. He's the sixth Flyers player to sustain a concussion this season.
- Jeff Carter was the last Flyer to score a natural hat trick on Nov. 11, 2010.
- Boston is 24-0 in games in which it has led by two goals at any point.
- The Bruins are heading to the White House to visit President Barack Obama on Monday.