Nick Foligno scored with 2.5 seconds left in the third period and Ottawa extended its winning streak to four games with a 4-3 victory Thursday.
Foligno put away a rebound of Daniel Alfredsson's slap shot for the winner after Florida's Kris Versteeg scored with 47.1 seconds left to tie it at 3.
"It was just good to get the win," Foligno said. "I don't think we wanted to do it in that fashion but we found a way to get it done and I think the guys are really happy right now."
Colin Greening scored at 17:53 to put the Senators up 3-2, setting the stage for the wild finish. Greening beat Jacob Markstrom with a wrist shot into the right side of the net with 2:07 left as Ottawa went on to even its record at 5-5.
"It's really disappointing," Panthers defenseman Brian Campbell said. "We feel we're a playoff team but we can't give away points like that."
Craig Anderson made 22 saves, and Alfredsson and Stephane Da Costa scored in the second period for Ottawa, which erased two one-goal deficits.
"You never know with this game," Anderson said. "As a goalie you've just got to make sure you make the next save. You can't worry about the score or what's going on around you. You just find a way to give the team a chance to win and let these guys go and score pucks in the other end."
Jason Garrison put Florida up 1-0 in the first, and Stephen Weiss restored the Panthers' lead at 2-1 in the second.
Markstrom stopped 34 shots in his second straight start.
"The game had some real see-saw, back-and-forth and momentum shifts throughout the game," Florida coach Kevin Dineen said. "At the end of it, it's not like we weren't prepared. We saw them do it just a week ago and knew we needed a 60-minute effort and felt that some sloppy play at the end really cost us."
Alfredsson, who missed the Senators' 3-2 shootout win at Carolina on Tuesday, tied it 1-1 on his fourth goal 5:27 into the second with a delayed penalty called on Florida.
Weiss gave the Panthers their second one-goal lead at 6:35 on a goal originally credited to Tomas Fleischmann.
Da Costa came out of the penalty box to draw Ottawa even for a second time at 14:14. The 22-year-old rookie center drove the left side and took Erik Condra's centering feed from the right corner.
"That was a great pass through a really tiny hole," Da Costa said.
Garrison opened the scoring 4:41 in when he drove a long slap shot past Anderson for his third goal.
Panthers D Ed Jovanovski left the game briefly after he was struck by a shot on the left hand early in the third. He returned after going to the dressing room. ... Florida went 0 for 4 on the power play. ... Senators coach Paul MacLean revealed earlier in the day that C Peter Regin's shoulder injury will sideline him for 6 to 8 weeks. Regin, who has one goal and two assists in five games, will not have surgery. ... Ottawa has been outscored 16-3 overall in the first period this season.