The rookie center scored twice, including the winning goal 1:50 into the extra period, as the Flames topped the Edmonton Oilers 2-1 on Saturday night.
Paul Byron won a battle behind the net 1:50 into the extra session and sent the puck in front to Monahan, who scored his 18th goal of the season and helped the Flames end a two-game skid.
"In overtime, (Byron) was just buzzing all over the puck and made a great pass to me which, fortunately enough, I was able to bury," Monahan said. "I was surprised that I had so much room. That was pretty awesome."
It was Monahan's first overtime winner in the NHL, and was the Flames' seventh win in their last 10 games.
"One thing we have learned about (Monahan) is that he doesn't miss too many of those chances around the net," Flames captain Mark Giordano said. "He has a knack for putting those ones in. Good on him. I am happy for him."
David Perron scored for the Oilers, who have lost three in a row.
"In our own zone, for the most part, I thought we were all right," Oilers coach Dallas Eakins said. "The last goal was just a great lesson for our defensemen there. You have to win the battle. It's a simple battle and that's what happens when you lose a battle like that, especially 4-on-4."
One especially troubling area for the Oilers of late has been the power play, which has now gone 0-for-19 in Edmonton's last six games.
"On the power play, we're having troubles entering and we're having troubles finishing," Oilers forward Jordan Eberle said. "On the one power play there, we must have had four or five chances and we couldn't capitalize. When that starts to happen, that starts to wear on you and you start doubting yourself.
"For me personally, the biggest thing with our lack of offence, and we seem to go through it every season, is that our power play is dead."
The Flames started the scoring just past the midway point of the opening period as Monahan was left alone in front of the net to coral a bouncing rebound and the Flames rookie sent the puck past Ilya Bryzgalov.
The goal was immediately followed by a heated fight between Edmonton's Luke Gazdic and Calgary's Kevin Westgarth, with Gazdic landing a punch that floored Westgarth, who had to be helped off the ice and to the dressing room.
"It was a good fight and both guys were throwing good punches," Giordano said. "At the end of the day, you care about the person and it is hard to see something like that. Hopefully he recovers quickly and can get back in the lineup. He is feeling all right now, which is good to see."
Edmonton came close to tying the game just over a minute later when a puck landed behind Reto Berra in the Calgary crease, but was quickly fished out by captain Mark Giordano.
The solid pace of the first period dropped off during a sloppy second period as Edmonton outshot the Flames just 5-3.
Calgary almost added to its lead seven minutes into the third period, but Giordano's shot rang off the post.
The Oilers tied it just before the midway point of the third as Perron emerged from the sideboards with the puck and fired a laser past Berra for his team-leading 23rd of the season. It was the first goal Edmonton had scored in just shy of 160 minutes of play, extending to before the Olympic break.
Edmonton picked up the pace for the remainder of the third, but the Flames held on to send the game to overtime.
Monahan said it was an important victory for the team coming off their eighth shutout of the season in a 2-0 loss to the Los Angeles Kings in their return from the Olympic break on Thursday night.
"It was kind of a must-win game for us," he said. "It was pretty intense. After (Westgarth) goes to war like he did, you have to find a way to win. Fortunately enough, we did. We just want to win as many games as we can at this point."
The Oilers were blanked 3-0 by the Minnesota Wild earlier in the week. The two Alberta-based teams are tied for the most shutouts allowed this season with eight apiece. ... It was the fourth of five games between the Oilers and Flames this season, with Edmonton holding a 2-1-1 edge. The Oilers have won six of the last 10 between the teams overall. ... The Oilers were without forward Nail Yakupov, who took a shot from teammate Justin Schultz off the foot in Thursday's loss to the Wild. While nothing was broken, there is no timetable for Yakupov's return. ... Flames defenseman Chris Butler was a surprise starter after suffering an injury against the Kings. Brian McGrattan, nursing an upper-body injury sustained in practice last week, has been cleared for contact but didn't play. Also out for Calgary were goalie Karri Ramo (lower body) and forward Curtis Glencross (lower body). ... Calgary forward Lee Stempniak took the game off to be with his wife after the birth of twin daughters Friday.