Among the many mysteries surrounding the Flyers is the one that concerns letdowns.

The Flyers have been markedly improved in the second half of the season. They're skating better. Their penalty-killing, a staple even when they were hideous, is outstanding. They are playing with confidence.

And yet they still collapse emotionally, as they did last night in a 6-3 loss to the Boston Bruins at the Wachovia Center.

After pushing the New York Rangers all over 33d Street and Broadway on Saturday, the Flyers looked flatter than Britney Spears' shaved head.

"We played tremendous the other night and I thought we would carry that into tonight, but the first thing we did" was pick up penalties, said Kyle Calder, who had a goal and two assists on Jeff Carter's line, with Scottie Upshall. "We have to find out a way around that. We have another [game] in less than 24 hours."

With Peter Forsberg gone and Mike Knuble out for at least a month, that's a tall order. Then Ben Eager left early with an ankle sprain last night. These things wear on a club.

"They came out strong and we came out kind of flat, and it was the kind of game without any emotion," Simon Gagne said. "And they had three goals off turnovers."

It was a one-goal game in the third period. Just over three minutes in, however, Brandon Bochenski fired high and beat goalie Antero Niittymaki, icing it at 5-3.

Bruins goalie Tim Thomas had a strong game, facing 33 shots but not many quality scoring chances. He made a difficult glove snare of Gagne's drive during a power play in the third period.

"That's one slapshot I remember," Thomas said. "I don't know exactly who shot it. . . . That shot made me look pretty good because [the puck] hit my glove pretty well."

Minutes later, Thomas slid across the crease to make an amazing save on Alexandre Picard.

While Thomas was terrific, Niittymaki gave up five goals on 17 shots after a strong performance against the Rangers. His inconsistency has hurt the club this season.

"It's not the year that he wanted to have," coach John Stevens said. ". . . His evaluation is tough. It's a tough thing for a goalie when you are chasing the game, and that's happened to us a lot this year."

The opening period was dreadful.

Yes, there were remnants of the Flyers' fury in Saturday's contest against the Rangers during several scrums.

But the Flyers took dumb penalties, such as when Joni Pitkanen slammed Marc Savard's head against the glass with a cross-check at 13 minutes, 23 seconds. That gave the Bruins a power play, and Savard made Pitkanen pay with a shot from the right circle that was redirected by Marco Sturm for his 19th goal and a 1-0 lead.

"I thought that first period, right from the face-offs, they were kind of dictating," Stevens said. "We were too soft on the puck."

There were six goals in the second period. Newcomer Scottie Upshall got a goal and an assist, giving him as many points with the Flyers (three) as he had all season in Nashville. His goal at 43 seconds tied the game.

"I'm getting to play with some great players right now," Upshall said. "Calder and Carter are great players, and I feel lucky to have the opportunity to go out in my first two games and jell with these guys."

Just over six minutes later, Carter scored from the high slot, giving the Flyers a 2-1 lead. But Niittymaki couldn't sustain it, as P.J. Axelsson retied the game just 34 seconds later.

The Bruins took over the remainder of the period, as Petr Tenkrat scored two goals in four minutes.

Contact staff writer Tim Panaccio

at 215-854-2847 or tpanaccio@phillynews.com.