Zegras was stopped on a penalty shot by Jordan Binnington at 2:51 of overtime after Philadelphia came back from two two-goal deficits in the third period.
Owen Tippett had a goal and three assists, and Christian Dvorak had two goals and an assist for the Flyers (9-5-3), who are 3-0-2 their past five games. Samuel Ersson made 12 saves.
Robert Thomas, Jordan Kyrou and Jimmy Snuggerud each had a goal and an assist, and Dylan Holloway and Justin Faulk scored for the Blues (6-8-4), who are 3-1-2 their past six games. Binnington made 25 saves.
Holloway’s third goal in as many games gave St. Louis a 4-3 lead just 40 seconds into the third period on a wrister from the left circle.
Thomas made it 5-3 at 4:56 off a one-timer from the slot when Snuggerud found him from behind the net. The shot grazed the leg of Philadelphia captain Sean Couturier.
Dvorak made it 5-4 at 7:53 after taking advantage of Blues defenseman Matthew Kessel slipping and losing the puck in the defensive zone, and Tippett tied it 5-5 at 10:29 on a shot high to the glove side after getting the pass from Zegras.
Kyrou made it 1-0 at 1:19 of the first period when he intercepted Zegras’ pass in the neutral zone, skated into the right circle and beat Ersson with a snap shot to the blocker side.
Zegras tied it 1-1 at 8:18 after the Flyers caught the Blues on a 3-on-2, with Zegras beating Binnington from the slot between the pads.
Snuggerud restored the Blues’ lead at 2-1 at 9:42, finishing off a Thomas pass with a wrister from the slot to the glove side.
Faulk’s slap shot from distance at 6:54 of the second period made it 3-1 after a face-off win. Cam Fowler’s assist on the goal was his 500th NHL point.
Dvorak came right back and made it 3-2 at 7:17, following up a rebound of a loose puck.
Zegras tied it 3-3 at 18:24 on a shot from near the blue line by Emil Andrae and tipped in front.
