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 night.
"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."
"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."
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.