Mangiapane scored his second of the game 46 seconds later when he went backhand-to-forehand on a breakaway at 12:56 to give the Flames a 4-0 lead.
"We had a good start," Mangiapane said. "We knew we needed to come out strong and get our legs underneath us. We scored on some early opportunities, and I think that was the difference in the game."
Zacha scored an unassisted goal after stealing a clearing attempt by Vladar in the bottom of the right face-off circle at 7:01 of the second period to make it 4-1.
Matthew Tkachuk gave the Flames a 5-1 lead with a power-play goal at 11:18 of the third.
Mercer made it 5-2 at 11:51, and Zacha scored a power-play goal with Wedgewood pulled for a 6-on-4 advantage at 17:01 for the 5-3 final.
"I think the compete, our speed, puck management, all the little details are on us to be better at the start of the game," Mercer said. "Calgary took advantage of that. I think as the game went on, we got better. In the third we really showed the type of team we are, but we've got to bring that all three periods of every game."
NOTES: The Devils played their third straight game without center Jack Hughes, who is on injured reserve because of a dislocated left shoulder. He will be reevaluated next week. … Mangiapane (seven) and Lindholm (seven) tied the Flames record for the most goals in the first six games of a season (Gary Roberts, 1991-92). ... Forward Johnny Gaudreau had one assist and needs one to tie Kent Nilsson (333) for eighth in Flames history. ... Calgary forward Blake Coleman, who played his first four NHL seasons with New Jersey and won the Stanley Cup with the Tampa Bay Lightning in 2020 and 2021, was honored with a video tribute in the first period. ... Devils defenseman Dougie Hamilton played a game-high 24:23 and had two assists, four shots on goal and two blocked shots.