"I'm sure it's very tough. He's a young guy coming in," Ottawa coach Guy Boucher said of Driedger, 22. "Everybody knows right now we've got some adversity. Our No. 1 goalie is out and our backup is out. I know the kid probably didn't expect to play and he comes in, and I'm sure it was tough, but it'll benefit him in the future."
Monahan one-timed a pass from Johnny Gaudreau by Driedger's blocker at 9:33 of the third period to give the Flames a 4-2 lead, and Frolik scored at 12:19 to make it 5-2.
Driedger, in his third NHL appearance, allowed four goals on 15 shots.
"I guess this is the third time I've been thrown in," he said. "The first two went a little bit better than this one. They can't all be perfect games, so I'm just trying to look to bounce back as soon as I can."
Hamilton beat Hammond to give Calgary a 1-0 lead 5:24 into the game, but Ottawa scored on consecutive shots on separate power plays to take a 2-1 lead.
Karlsson tied it 1-1 at 11:31, and Turris shot from the top of the left faceoff circle by Elliott to put the Senators up 2-1 at 14:51.