Giroux scored on a deflection off Matt Carle's pass to beat Antti Niemi and win the third straight one-goal game in the series.
Twice, the Philadelphia Fly Guys needed video replay to decide if a goal counted.
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One did, one didn't.
Giroux didn't need the officials to check his winner.
Giroux ended the game moments after Simon Gagne thought he scored the winner, only to have replay officials rule the puck didn't cross the goal line.
It was the second time replay was needed to determine a Flyers' goal. They went 1 for 2 -- but, oh, how huge that one was for the Flyers in their first Stanley Cup home game since 1997.
Scott Hartnell had a no-goal overturned by replay to spark the Flyers to their first Cup win since 1987. Danny Briere and Ville Leino also scored for the Flyers, helping them win a game they desperately needed to avoid their second 3-0 hole of the playoffs.
Michael Leighton made 24 saves for the Flyers. Niemi stopped 28 shots in the third straight thriller in the series.
The game was hard fought from the start and by the third period many players seemed to be huffing and puffing up and down the ice.
Chicago and Philadelphia swapped goals 20 seconds apart to make it 3-3 early in the third. Patrick Kane was all alone on a breakaway when he beat Leighton stick side for his first goal of the Stanley Cup final and Chicago's first lead, 3-2.
Leino then revived a suddenly hushed crowd when his rebound off Giroux's shot tied it 3-all.
Kane had the assist for his first point of the series and make it 1-1. The goal was one of the few times the decibel level at the Wachovia Center returned to easy-listening levels.
In the first Stanley Cup finals game at the Wachovia Center since Game 2 of the 1997 final, the crowd was unglued from warmups. The rocking sellout crowd of 20,297 was the largest to ever watch an NHL game in Pennsylvania.
The Flyers seemed determined to win it in regulation and pounded Niemi in the third. He delivered by stopping 14 of 15 shots.
The Flyers improved to 8-1 at home this postseason.
Duncan Keith, Brent Sopel and Kane scored for the Blackhawks.
The Blackhawks, trying to win their first Stanley Cup title since 1961, snapped a seven-game winning streak and a seven-game road winning streak.
Game 4 is Friday night in Philadelphia.
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