Updated

CHICAGO (AP) — Chris Pronger and Philadelphia's stiff defense suddenly went soft, and the Flyers are facing elimination.

After pushing Dustin Byfuglien and the Chicago Blackhawks around for the better part of the Stanley Cup finals, Pronger and his blueline mates ran out of steam in the 7-4 loss on Sunday night.

Pronger, Matt Carle, Braydon Coburn and Kimmo Timonen were so good in front of goalie Michael Leighton while the Flyers won Games 3 and 4 and stormed back in this series. With the United Center crowd going eardrum-cracking crazy, however, the Blackhawks came out with a bundle of energy and scored three times in a six-minute span late in the first period.

The Flyers never recovered.

Frustrated for the better part of the first four games, the 257-pound Byfuglien — moved to a different line as part of a major shuffle by coach Joel Quenneville — finally scored and got some revenge on the pesky 6-foot-6 Pronger.

The NHL postseason leader in defenseman scoring with four goals and 13 assists entering this game, Pronger has been squarely in the discussion for the Conn Smythe Award as the MVP of the playoffs if the Flyers can win their first Cup since 1975. He had a plus-7 rating over the first four games, and he averaged more than 29 minutes of ice time per game.

After playing only six of his previous 21 postseason games in the red, though, Pronger was on the ice for six of Chicago's goals. His penalty led to the other one.

Pronger spoke before the series started about making Byfuglien work in front of the net and not simply letting his linebacker-like body camp in front of the crease as Pronger insinuated previous Blackhawks opponents let happen.

Well, Byfuglien was as active as he's been in two weeks, even finding an opportunity to knock Pronger off his feet and onto the ice with a lowered shoulder near the corner midway through the second period.

The hit song "How You Like Me Now?" by The Heavy got a little airplay at the arena a few seconds later.

Then with 4:42 left in the second period, Pronger was called for hooking on Patrick Kane. Booed all night by the red-clad crowd, Pronger drew more jeers when he was shown on the video board sitting in the penalty box with a gap-toothed grimace.

Just 27 seconds later, Byfuglien got his first goal of the series.

Parked by the crease without Pronger to push him out, Byfuglien caught a break when Coburn slipped and couldn't stop the pass from Jonathan Toews. Byfuglien tapped in the puck for a 5-2 lead, his face wearing a look of relief when shown on screen.

Then came the ultimate insult, with 2:05 left and an empty Flyers net. Byfuglien flipped a puck past Pronger that had enough on it to wiggle down the ice and into the goal.

Pronger was a big — literally — reason why Chicago's top line of Toews, Kane and Byfuglien were so unproductive in the first four games. By splitting them apart, Quenneville made it impossible for Pronger to follow them all around.

Maybe it was the home-ice advantage, complete with Michael Jordan wearing a Toews jersey in the seats, or maybe it was just an off night, but the Flyers didn't have the same spark that they showed even in losing Games 1 and 2 here.

They looked frustrated, even taking the retaliatory penalties they smartly avoided in most of the first part of the series.

Leighton was pulled after the first period, the second time coach Peter Laviolette made an in-game goalie change in this series.

The home team was sloppy in the middle of the game, but the Hawks had too big of a lead and too much momentum on their side for the Flyers to take advantage of it.

Leighton sure wasn't at his best, but Chicago's first goal — by defenseman Brent Seabrook — glanced off Pronger's skate when he tried to close his legs and block the shot. It slipped between Leighton's blocker and the side of the net.

Later, after Scott Hartnell scored to give the Flyers their first goal early in the second period, Kane answered for the Blackhawks to stretch the lead to 4-1.

Pronger couldn't block Andrew Ladd's pass, and neither Carle nor center Danny Briere tracked Kane who got loose and sent an across-the-slot pass from Ladd into the net past Leighton's sub Brian Boucher.