Panthers goaltender Scott Clemmensen stops a shot by Marcus Johansson of the Capitals during Florida’s 5-4 victory. (Joel Auerbach/GETTY IMAGES)

The Washington Capitals have won the Southeast Division each of the past four seasons. But their reign will be tested this winter by Florida — a point the revamped Panthers hammered home Monday.

Stephen Weiss registered two goals and an assist, and the Panthers struck three times on six power-play opportunities to hold off the Capitals, 5-4, at BankAtlantic Center.

The defeat dropped Washington seven points behind Florida, which is off to its best start since 1999-2000, the last season the Panthers made the playoffs. The Capitals, meantime, fell to 1-3 under Coach Dale Hunter.

Jason Chimera scored his team-best 11th goal with 1 minute 44 seconds left to play to trim the visitors’ deficit to one goal. But their frantic comeback attempt in the closing seconds — with goalie Michal Neuvirth on the bench for an extra attacker — wasn’t enough for them to overcome a wretched start in which the Panthers raced to a 5-1 edge in the second period.

“We have to have the third-period effort in the first period and run that for 60 minutes,” said Brooks Laich, who also scored in the third. “What we’re doing right now is unacceptable. It’s not acceptable to play hockey for 20 minutes and not execute for the other 40. We’re not here to try, we’re here to win.”

Neuvirth made 25 saves for the Capitals in an uneven effort. Panthers goalie Scott Clemmensen struggled as well, finishing with 28 saves.

The unsightly defeat came on a day of intrigue in South Florida.

It began with the surprising news that Tomas Vokoun, the Capitals’ No. 1 goaltender, would not be starting in his return to Florida, which was followed by some pointed words from the disappointed netminder.

Vokoun played the previous three seasons for the Panthers and shut out his former team at Verizon Center, 3-0, on Oct. 18. But Hunter turned to Neuvirth, who made 32 saves in Saturday’s 3-2 win over Ottawa.

“Those are the decisions coach makes,” said Vokoun, who traveled and stayed separately from the team so he could spend time with his wife and two daughters, who still live in Fort Lauderdale. “I’m a paid employee and I don’t make those kind of decisions. I’m a hockey player and I’m here to play games.”

Alexander Semin, meanwhile, participated in the morning skate but missed his second straight game. On Saturday, the struggling winger sat out with a right shoulder injury. His status on Monday was much harder to figure out.

After the morning skate, Hunter said: “He’s ready to go. So we’re going to make a game-time decision who’s going to sit out.” A team spokesman said before the game that Semin remains day-to-day with an undisclosed injury.

Against the Panthers, the Capitals were blitzed during a penalty-filled opening 20 minutes. Mathieu Perreault, Troy Brouwer and Karl Alzner all took penalties, as did John Erskine, who was assessed an instigator, a fighting major and a 10-minute misconduct after responding to a hit on Jeff Halpern.

“The refs called them,” Hunter said. “Doesn’t matter if it’s right or wrong in my eyes. It’s their eyes that counts.”

Weiss opened the scoring on the power play at 6 minutes 50 seconds of the first period with a shot that appeared to hit defenseman Dennis Wideman before eluding Neuvirth.

Only 13 seconds later, Mike Santorelli fired a knuckling shot past Neuvirth’s blocker to put the Panthers ahead 2-0. It was Santorelli’s fifth goal in seven career games against the Capitals and, more important, was another stoppable shot that has plagued both Washington netminders in recent weeks.

“That was a knuckler,” Hunter said. “If you watch it on tape, it was like Phil Niekro coming in there. It was dipping and diving.”

Neuvirth rebounded to make a pair of highlight-reel stops on Kris Versteeg and Sean Bergenheim. But he couldn’t stop a power play point blast from Dmitry Kulikov, who put the Panthers ahead, 3-0.

Mike Knuble scored his first goal in 15 games to cut the Capitals’ deficit to 3-1 after ripping a slap shot past Clemmensen 2:49 before the first intermission. But it was only a temporary reprieve from a game the Capitals would just as soon forget ever happened.

Rookie defenseman Dmitry Orlov took a slashing penalty only moments into the second period, and Bergenheim scored the ensuing power play to make it 4-1.

Weiss’s second goal of the game put the game out of the Capitals’ reach, 5-1, at 12:11 of the second period. It also embodied Washington’s struggles. The play was set up by former Capitals winger Tomas Fleischmann, who danced through the middle before threaded a pass through Alex Ovechkin (minus-2, zero points) to Weiss.

“We were watching the puck too much,” Alzner said. “Kind of the same thing happened on their fifth goal — ultimately it was the winner. We were all kind of watching Fleischmann do his thing out there, and that’s what happens.”

Late goals by Laich and Chimera gave the Capitals hope. But said there was no silver lining in his team’s effort.

“If you want to be a professional,” Laich said, “you judge yourself by results not by your intentions.”