Up 3-2 in the third, the Senators gave up four unanswered goals to lose their fourth game in a row.
The Ottawa Senators have extended their four-game losing streak, falling 6-3 to the Calgary Flames on Tuesday night. After 40 minutes, Ottawa led 3-2 before the Flames torched them for four goals in the third. Blake Coleman and Yegor Sharangovich each scored twice for Calgary.
Joonas Korpisalo made 30 saves in the loss as the Senators fell to 14-22-0 on the season.
The Sens opened the scoring at 4:09 of the first period. Calgary native Jacob Bernard-Docker scored in his return home on a point shot that deflected in off Calgary's Yan Kuznetsov.
The Senators' lead didn't last long. Less than a minute later, Connor Zary picked up the puck after a failed Jake Sanderson clearing attempt and fired home a wrist shot over Jakob Markstrom's glove.
The first period ended on a high for the Senators, who made it 2-1 with three seconds left in the period when Dominik Kubalik neatly tucked home a rebound past a sprawling Jacob Markstrom.
Early in the second, Calgary tied things up on a goal by Yegor Sharangovich, who took an excellent feed from Jonathan Huberdeau and snapped a shot, top shelf, past Korpisalo.
Heading into the game, Senators head coach Jacques Martin swapped out Tim Stutzle for Claude Giroux on the top power play unit.
It paid dividends at 12:39 as Giroux made a nifty backhand deke next to the Flames' net and quickly found Brady Tkachuk, who ripped a shot past Markstrom.
Calgary wouldn't go away, though. The Flames tied things yet again 47 seconds into the third period. Noah Hanifin aggressively jumped up from the blue line and scored on a backhander as Zary screened Korpisalo.
At 8:57, Calgary took the lead for the first time in the game when Blake Coleman gently retrieved the puck in front of the Senators' net after a blocked Hanifin shot. Coleman patiently deked out a lunging Korpisalo to score.
The third-period collapse worsened when Sharangovich scored his second goal of the game to give the Flames a 5-3 lead. Sharangovich tucked away a point shot that was blocked by Jakob Chychrun, only for the puck to go right onto Sharangovich's stick for an easy goal. Coleman added an empty netter to seal the 6-3 win for the Flames.
The Senators return to action on Thursday night when they play the Buffalo Sabres at 7 pm to close out another ill-fated five-game road trip.