VIDEO: Sabres' Johnson makes spectacular save to set up OT winner
Girgensons' overtime winner was his first goal since Feb. 24.
Johnson made 30 saves in the victory as the Sabres improved to 3-6-0 on the season. They'll play the Pittsburgh Penguins on Thursday.
The Flyers, who fall to 4-2-2, salvaged a point when Brayden Schenn tipped a Claude Giroux shot past Johnson to tie the game with 53.2 seconds remaining. They will look to get back on the winning track against the New Jersey Devils.