Sean Pollock scored the game winning goal for Colorado at 9:10 of overtime from veteran John Grant Jr. and Joel Dalgarno.
The Mammoth improve to 5-7 and the Roughnecks drop to 6-4.
Calgary blew a 5-0 lead in the contest, only to see the Mammoth march all the way back and tie the game at 5-5 by halftime.
Grant Jr., who is one of the best lacrosse players in the history of the National Lacrosse League, led Colorado in scoring with a goal and five assists for six points. He also collected a game high 11 loose balls.
The major story in the NLL at the moment is the play of the Edmonton Rush, who are a perfect 9-0. They become the first team in NLL history to win the first nine games of the season after their 10-9 win over the Vancouver Stealth Saturday.
The Roughnecks will try to end the Rush streak when they host Edmonton in their next game on Friday, March 14 from the Scotiabank Saddledome in Calgary.