The 257-pound Byfuglien, who had eight goals in the first three rounds of the playoffs but none in the first four games against a tough Flyers defense, had a power-play goal in the second period and an empty-netter in the closing seconds.
"Getting down there two games in their building, we had to come back with some fire and get on them and show them we weren't going to quit," Byfuglien said. "Right from the get-go, we moved our feet and were physical."
Byfuglien's top line that had included Patrick Kane and Jonathan Toews was split up for Game 5, a strategy that worked for coach Joel Quenneville. They had combined for just one goal and four assists in the first four meetings with Philly. Kane also had a goal and an assist, and Toews added an assist.
Brent Seabrook added a power-play goal, and Dave Bolland, Kris Versteeg and Patrick Sharp also scored for the Blackhawks, who can capture the Stanley Cup for the first time since 1961 with a victory Wednesday night in Philadelphia in Game 6. A Flyers win would send the series back to Chicago for Game 7 on Friday night.
"We're not going to think about that now. We have to keep levelheaded and go into that building with the same mind-set and have fun," Versteeg said of the chance to wrap it up.
All five wins in the series have come on home ice.
Scott Hartnell, Kimmo Timonen, James van Riemsdyk and Simon Gagne scored for the Flyers. Gagne's goal with 2:36 left made it 6-4, but a half-minute later, Byfuglien converted the empty-netter. "We got outworked pretty good," Flyers coach Peter Laviolette said.
The Blackhawks blitzed goalie Michael Leighton with three goals in the final 7:43 of the first period, and United Center erupted as Chicago quickly found the offensive game that had helped it make the Finals.
Leighton was pulled after giving up three goals on 13 shots in the first period.
Kane, who had been with Byfuglien on a struggling Blackhawks first line that Quenneville split up, got his second goal of the Finals on a nice pass from Andrew Ladd. Ladd had his shot blocked by Flyers defenseman Chris Pronger, recovered the puck and passed it to Kane, who streaked to the net uncovered to beat Brian Boucher for a 4-1 lead.
Pronger finished with a minus-5 in Game 5.
In the 20 previous Stanley Cup Finals tied 2-2, the club winning Game 5 has won the Stanley Cup 14 times. Last year, the Pittsburgh Penguins were one of the six teams to overcome a loss in Game 5 after the series had been knotted at 2-2.