Washington, which lost for only the third time in 20 games (16-3-1), had clinched the top seed in the Eastern Conference on Friday when Philadelphia lost to Buffalo.
The Capitals will open the playoffs against the New York Rangers, who landed the final postseason berth in the East when Carolina lost at home against Tampa Bay.
"It's the 82nd game, to be honest, I think we were looking ahead," said Capitals forward Mike Knuble. "At times we were tired and at times we were sloppy."
Knuble admitted some of the Capitals players were doing some scoreboard watching during the game, eager to find out who they would face in the playoffs.
Despite Washington having nothing at stake, Alexander Ovechkin and the other Capitals stars played in the team's season finale. The one exception was defenseman Mike Green, who sat out his 20th consecutive game since sustaining a head injury on Feb. 25. Green had been expected to make his return to action on Saturday.
Michal Neuvirth made 22 saves for the Capitals.
"We didn't have a lot of polish," said Washington coach Bruce Boudreau. "I thought we were very, very sloppy today. I think that comes with the mindset of a 'Let's get this over with' type thing. It's over, so there's no reason for that to happen anymore."
The Capitals went 1-2-1 against the Rangers this season, with the two regulation losses coming by scores of 7-0 and 6-0.
"We're ready for anybody," said winger Matt Bradley. "We're excited to play in New York and Madison Square Garden and ready to get it going."
For the Panthers, the victory was their first since a 4-0 shutout over Toronto on March 17 and it helped them avoid matching the NHL's longest season-ending slide since the 1967 expansion. The 2003-04 Los Angeles Kings and 1976-77 Detroit Red Wings both ended the season with 11 consecutive losses.
"It was a nice way to end, for sure," said center Stephen Weiss, who returned to action after missing three games with a groin injury. "It's been a rough month or so. It's nice to get a win at home for the fans."
Vokoun, making perhaps his last start for the Panthers, made a triumphant return after missing five games because of a back injury. Vokoun, whose contract expires after the season and who'll be a free agent, recorded his sixth shutout of the season.
"I thought he was outstanding," said Panthers coach Pete DeBoer. "He was rested and he wanted to play tonight. He showed a lot of character coming back from an injury and getting himself ready, and I'm sure in the back of his mind he's wondering if this is his last game here. Hopefully, he's back. And if he's not, I think it's a fitting way for him to end his time in Florida."
Most of Vokoun's best stops came against Ovechkin, including a blocker save with 3:25 left in the third period.
Thomas broke the scoreless tie with a fluky goal right off a faceoff. After Patrick Rissmiller's pass was tipped, Thomas swung and hit the puck out of the air and it bounced between Neuvirth's legs.
"A win is a win and obviously a shutout is nice," Vokoun said. "You knew when halfway through the game it's 0-0 it's going to be one of those games where one goal is going to decide the game. And it was. At least for once we were on the winning side."
- The loss prevented Washington from matching its record for most road victories in a season (24), set last year.
- Washington rested veteran C Jason Arnott for the second consecutive time this week.
- The teams ended up splitting their six-game series.
- C Stephen Weiss, Florida's leading scorer, returned after missing three games because of a groin injury.