"We knew the game was all about don't stop believe we can still win the game," said Ovechkin, who was criticized on Wednesday by former Caps goaltender Olaf Kolzig for being "wrapped up too much in the rock star status" and then was involved in a skirmish with teammate Dennis Wideman at Thursday's practice.
On top of that, the Capitals were riding a three-game losing streak and in danger of falling six points behind Florida in the Southeast Division standings. Making the game even more important was the fact it began a stretch of five games in nine days that includes two back-to-backs.
The victory in front of 17,779 at the BankAtlantic Center cut Florida's lead to two points. Both teams have 25 games remaining, including a rematch April 5 at Washington.
"We needed this win, we would be in big trouble if we didn't win," goalie Tomas Vokoun said. "It's a huge win for us."
Vokoun made 22 saves in his return to the BankAtlantic Center, where he played his home games the last four seasons. Vokoun shut out Florida twice this season, but both games were at the Verizon Center.
"A big game, I was a little nervous, too," Vokoun said. "It's not easy playing back where I played last year, and we're chasing them. But I settled in and (it was) obviously a great finish by our guys."
This was the first time in five meetings the road team won. Michal Neuvirth was in net for the Capitals when they lost at the BankAtlantic Center on Dec. 5 (5-4) and Feb. 1 (4-2).
In his first start against his former team, Florida goalie Jose Theodore finished with 39 saves. Theodore spent two seasons with Washington before moving to Minnesota in 2010-11 and then joining the Panthers last summer; he had yet to face his former team.
Theodore, who got the start after Scott Clemmensen was pulled from Wednesday's 6-2 loss against Ottawa, made several spectacular saves in the first two periods. Among them were a stick save on a Jeff Halpern shot from a sharp angle and a kick save on Halpern's one-timer from the right faceoff dot.
"He was great all game for us," Florida defenseman Brian Campbell said. "He's been great all season. He was always there for us. We would have liked to have gotten him a couple more to help him out there."
It was the first time this season the Panthers lost in regulation when leading after two periods; they had been 16-0-4 when taking a lead into the third period.
"When you have a lead, you try to at least get a point out of it, but we found a way to lose tonight," forward Kris Versteeg said.
Semin scored the game-winner with 6:33 left with a slap shot from the top of the right circle that handcuffed Theodore after it quickly went off the stick of Sean Bergenheim.
Florida carried a 1-0 lead into the third period until Ovechkin scored a power-play goal at 4:47. With Mikael Samuelsson in the box for slashing, Ovechkin scored from a sharp angle after grabbing a loose puck.
The goal occurred with Florida defenseman Mike Weaver injured on the ice after he was hit in the face by the stick of Mike Knuble after going down to make a play. Weaver stayed down for several seconds after the play and had to leave the ice, although he returned a few minutes later.
"Even though the whistle should have blown, they ended up getting one on their power play," Florida coach Kevin Dineen said. "A guy gets hit in the face and then we've got possession of the puck, but you know what, that's something that the officials will hopefully take a look at and they'll be better on something like that and not make those kind of mistakes in the future."
It was one of four power plays for Washington in the third period; Florida had none.
"I don't think we had a great second period and then we got into penalty trouble in the third and couldn't stave off all those opportunities that they were given," Dineen said. "It was the difference in the hockey game."
The Capitals appeared to have tied the score in the final minute of the second period when Brooks Laich's shot from the top of the left circle got by Theodore, but was the goal was immediately waved off. Knuble, playing after being a healthy scratch the previous three games, was called for goalie interference after making contact with Theodore in the blue paint.
"We had a goal disallowed, and that's always tough," Capitals coach Dale Hunter said. "But the guys were ready to play tonight. They played hard and they wanted to win bad."
Washington came close to breaking a scoreless tie on a power play late in the first period when Dmitry Orlov's wrist shot from the high slot beat Theodore but hit the crossbar and stayed out.
Fleischmann scored with 39.8 seconds left in the first period after a nice setup from Stephen Weiss. Weiss skated the puck behind the Washington net before slipping a backhand pass to Fleischmann through the legs of Ovechkin. Fleischmann one-timed the pass from inside the left circle and beat Vokoun to the stick side.
The goal extended Fleischmann's points streak to five games, during which he has two goals and four assists.
But the Panthers couldn't get anything else past Vokoun, who has stopped 84 of 85 shots against his former team this season.
"They were in pretty good position all night," Versteeg said of the Capitals. "We tried to get plays. I don't really know what to tell you, but they did a good job in the (defensive) zone."
The game finished with one linesman after Andy McElman sustained a broken nose when he was hit by a puck in the third period. McElman was injured when Erik Gudbranson attempted to shoot the puck down the ice while Florida was killing a penalty. He was knocked to the ice, but immediately got up and leaned over the Washington bench, kicking the boards in pain. He didn't return to the game.
1 - 0 FLA
1 - 1 Tie
2 - 1 WSH
Delaying Game-Puck over glass
Interference on goalkeeper