It was Philadelphia's second straight victory after losing its first nine games to start the season.
Noel Acciari scored his first goal of the season, and Trevor Zegras had three assists for Philadelphia (2-6-3), which began the season 0-6-3 before defeating the Ottawa Senators 3-1 on Saturday. Joseph Woll made 24 saves.
Martin Necas and T.J. Hughes scored for Colorado (5-3-1). Mackenzie Blackwood made 21 saves.
Michkov scored a power-play goal to give the Flyers a 1-0 lead at 7:41 of the first period. Michkov dug a puck out of the corner on the right side and passed across to Zegras, whose slap pass hit Flyers forward Denver Barkey in front before popping back out to Michkov, who shot into an open net from below the right circle.
The goal stood after the Avalanche challenged the play for goaltender interference.
Michkov then made it 2-0 at 12:23 of the second period. He circled the offensive zone before scoring with a shot from above the circles that went through traffic and past Blackwood.
Necas scored three seconds after a power play expired to make it 2-1 at 17:52. Artturi Lehkonen found Necas open above the right face-off circle, and he roofed a shot through traffic over Woll's blocker.
Acciari pushed the Flyers' lead to 3-1 at 6:34 of the third period, redirecting Oliver Bonk's slap shot from the right point. It was Acciari's first point in 11 games with the Flyers.
Hughes cut it to 3-2 14:40 of the third. Sam Malinski's shot from the right point went off the stick teammate Fedor Svechkov and deflected to Hughes, who scored from the right face-off circle.
