Ottawa was expected to pick up its game after general manager Bryan Murray and coach Paul MacLean addressed the team following a loss to New Jersey on Wednesday.
But on Thursday the Senators came undone with a poor third period and a late collapse that ended in a 4-2 loss to the Florida Panthers.
Tom Gilbert and Tomas Kopecky each scored in the final three minutes as the Panthers won their fifth straight game and seventh in their past eight.
"I thought we had a good response from (Wednesday) night's game," MacLean said.
"I liked the start of the game. We played (Wednesday) and they were sitting here waiting for us so we expected they would carry it a little bit until we got our legs. The second period I thought we wasted some of our energy and that fatigue didn't help us in the third."
Gilbert beat Senators netminder Craig Anderson with a one-timer on a pass from Tomas Fleischmann at 17:28 of the third period with only two seconds remaining on a high-sticking penalty to Senators forward Jean-Gabriel Pageau.
One minute later, with the Senators on a power play, Erik Karlsson fell in the Panthers' zone allowing Kopecky to break out 2-on-1. He elected to shoot and beat Anderson at 18:19 with the insurance goal.
Jimmy Hayes, in the first period, and Aleksander Barkov, in the second, also scored for the Panthers (14-17-50), who got a 32-save performance from Scott Clemmensen.
"It was a good effort by everyone and a good road game for us," Clemmensen said.
"We had a game plan and we stuck with it. This team is playing with a lot of confidence right now. We went down in the first but we stuck to it and believed in the game plan and that's probably the biggest difference between now and the beginning of the year."
At the beginning of the year the Panthers won just three of their first 16 games and it cost head coach Kevin Dineen his job. Peter Horachek took over and his first game at the helm was a 3-2 loss in Ottawa on Nov. 9.
Coincidentally that was the last time Ottawa had won consecutive games.
"At that point I was just opening the doors," Horachek said of that first game.
"I was just telling them how I feel the team should play and I think they wanted to play hard with a new coach. The structure and the confidence wasn't there and now the guys know they are capable of winning in whatever building they are in. We have to play our game and not bend around and see how other teams are going to play."
Chris Neil and Jason Spezza scored for the Senators (14-17-6), who have now lost two straight and three of their past four.
"We just didn't do enough to win. We got too passive and found a way to lose," Spezza said.
"It's clear we're feeling pressure now and we're feeling the heat. We're trying to win hockey games and the effort is there but we don't execute and we don't play loose enough with the puck and we're making mistakes at the end. That's the position we've got ourselves in and we have to find a way to get out because no one is going to give us any help."
Both teams took turns taking and giving away the lead through the first two periods, starting with the Panthers.
Hayes opened the scoring with his fourth goal of the season as he beat Anderson from the right hash mark at 5:39 of the first period.
After a review to see if the puck was kicked in, Neil was credited with the tying goal at 9:17 of the period. Clarke MacArthur took the original shot but after Clemmensen made the save the puck bounced in of Neil's skate for his fifth goal of the season.
The Senators took the lead in the final minute of the period when Spezza made a sensational play, first getting the puck around Panthers defenceman Dylan Olsen at the face-off circle then beating Clemmensen high and on the short side with very little space.
It was Spezza's 11th goal of the season and first in his past 13 games.
Barkov tied the game for the Panthers at 17:11 of the second period with his sixth of the season when he redirected Gilbert's shot past Anderson.
The Senators were also forced to play the final two periods without forward Mika Zibanejad who left after only five shifts and 2:38 of ice time with an upper-body injury.
Notes- Defencemen Patrick Wiercioch and Eric Cryba, along with forward Cory Conacher were scratches for the Senators. Defenceman Mike Mottau and forward Scott Gomez sat for the Panthers ... The Ottawa Senators have allowed 42 first-period goals this season, the most in the NHL. Going into Thursday, the Senators had the most penalty minutes in the league with 164 and were only 24th with a 78.9 per cent efficiency on the penalty kill.