McMann and Ville Ottavainen scored in regulation, and Philipp Grubauer made 24 saves through overtime and stopped four of five attempts in the shootout for Seattle (5-2-0).
Christian Dvorak and Trevor Zegras scored for Philadelphia (0-5-3), which lost its eighth straight game to open the season. Dan Vladar made 29 saves through overtime and stopped three of five shooters in the tiebreaker.
McMann scored a power-play goal to give the Kraken a 1-0 lead at 7:57 of the first period. Jordan Eberle carried the puck to the net from the goal line on the left side of the Philadelphia zone, but Flyers defenseman Simon Benoit knocked it off his stick. The loose puck caromed to McMann in the right slot, and he scored to the short side over Vladar's shoulder.
Eberle was stopped on a penalty shot attempt at 6:23 of the second period. He skated through the crease and around Vladar's poke check attempt, but the Flyers goalie was able to step back and use his right pad to deny the Kraken captain.
Ottavainen's first NHL goal made it 2-0 at 8:54 of the second period. The rookie defenseman, in his fourth game this season, snapped a shot from between the top of the circles that went through a screen by teammate Matty Beniers.
Dvorak cut it to 2-1 at 6:07 of the third period. Oliver Bonk skated the puck the length of the ice and sent a cross-ice backhand pass to Dvorak, who snapped a shot from the right side.
Just 1:13 later, Zegras tied it 2-2 with a 4-on-4 goal at 7:20. Travis Sanheim skated the puck into the offensive zone, stopped at the post and found Zegras joining the rush for a one-timer from the slot.
