BUFFALO, N.Y. - Philadelphia Flyers forward Sami Kapanen hit the post in overtime. Peter Forsberg missed an open net. So did Mike Knuble, his shot smothered by Buffalo defenseman Jay McKee.

While goaltender Robert Esche did his part, stopping a career-high 55 shots, Philadelphia’s offense has to improve if the Flyers intend to rebound after losing the opening game of their first-round Eastern Conference playoff series against the Sabres.

“I think the concern is you don’t want to waste a great performance by a goalie,” Flyers coach Ken Hitchcock said on Sunday, a day after his team’s 3-2 double-overtime loss. “We got that type of performance. But we didn’t execute offensively for him.”

Not even close. Game 2 is at Buffalo on Monday.

Although they rallied from a 2-0 deficit to force overtime on Simon Gagne’s goal in the final two minutes, the Flyers’ offensive troubles were numerous. Philadelphia registered just 32 shots — and only 21 through regulation — had 27 shots blocked and had another 23 miss the net entirely.

Philadelphia couldn’t get going at the start of the first three periods, failing to register a shot in the first nine minutes of each frame.

It didn’t help that the Flyers’ top line of Forsberg, Gagne and Knuble, generated the bulk of the scoring chances and accounted for both goals.

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“That’s something we’ve got to get better at,” said Kapanen, who beat goalie Ryan Miller with a backhander from in close, only to have the shot deflect off the post 13 minutes into the first overtime. “I think I should be one of the guys and I want to be one of those guys providing some offense.”

The Sabres also could make a case regarding lack of production, considering they scored just three times — capped by Daniel Briere’s tip-in 27:31 into overtime — on a franchise playoff-record 58 shots while going 0-for-9 on the power play.

“Our finish,” Sabres coach Lindy Ruff said, referring to what his team needs to improve. He lamented that his players tried to be too creative, turning down chances to shoot by instead making an extra pass.

Then again, Ruff will take the victory, an important one for a young team that weathered a scare after making its first playoff appearance in five years.

“I think it would’ve been a very big disappointment if we didn’t win,” Ruff said. “You don’t know what (a loss) would’ve done to the psyche of a young team. But to win, that lifts everybody.”

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The Sabres have plenty of reasons to feel good, having won six straight and eight of nine. They also showed the ability to stand their ground against a more physical opponent.

That was emphasized by one hit, when lightweight defenseman Brian Campbell leveled Philadelphia rookie R.J. Umberger with a heavy — but clean — open-ice check 12 minutes into overtime. A woozy Umberger, whose nose was bloodied, lay on the ice for several minutes before being helped to the locker room.

Remarkably, Umberger said he only sustained a stiff neck and said he could play on Monday.

“I got my wits back real quick,” Umberger said. “I lost a little bit of quick memory, but otherwise I felt fine. I wanted to go back out last night, but they wouldn’t let me.”

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Campbell lowered his right shoulder and hit Umberger across the chest and jaw, catching the player with his head down after Umberger took a pass inside his own blue line.

“It was a legal hit,” said Umberger, who has watched the replay once. “I didn’t expect him, especially him, Campbell, to step up right there.”

Campbell was happy to learn Umberger was OK.

“I was just trying to step up and make a play and it ended up being a pretty good hit,” Campbell said.