The Bruins (41-27-13) trail the Ottawa Senators by two points and the Pittsburgh Penguins by one for a wild card from the Eastern Conference. Boston and Ottawa each have one game remaining; Pittsburgh has two.
"It's tough," Bruins center Chris Kelly said. "We've been a proud group that's always wanted to do things on our own and we're looking for help."
Boston plays at the Tampa Bay Lightning on Saturday night. Ottawa visits the Philadelphia Flyers that afternoon. The Bruins' loss clinched a playoff berth for the New York Islanders, who did not play Thursday.
"We shoot ourselves in the foot and we've put ourselves in this position now that you have to win the next game, no ifs or buts, and you have to hope you get some help," Bruins coach Claude Julien said. "We were hoping we wouldn't be in that position where you rely on others. Right now, we are. …We have to look at ourselves, nobody else."
The Panthers scored three consecutive goals, two in the third period, to take a 3-1 lead.
Aleksander Barkov tied it 1-1 with 1:20 left in the second period, and Jonathan Huberdeau gave Florida a 2-1 lead with a backhand 4:02 into the third on assists from Jaromir Jagr and Brian Campbell. Jagr's second assist gave him 1,800 NHL points; he passed Ron Francis for fourth all-time.
Brad Boyes scored at 8:03 for a 3-1 Panthers lead.
"They have to win now, but this was more about us showing up now that we're out of it," Panthers forward Shawn Thornton said. "... I really wanted to win this game. It feels good in here.''
"As long as I've been here, that's one thing that's defined the Bruins: Being able to play their best hockey at the most important times," Kelly said. "Tonight, that third period wasn't the usual Boston Bruins you've seen in the past."
Bruins goalie Tuukka Rask was 12-1-1 with a 1.12 goals-against average and .960 save percentage against the Panthers. He made 26 saves Thursday.
The Bruins scored first on Patrice Bergeron's power-play goal with 4:58 left in the second period, eight seconds after Willie Mitchell was sent to the penalty box for interference. Camped in front, Bergeron stuck in a rebound stick-side past Panthers goalie Roberto Luongo.
The Panthers tied the game on their power play 3:38 later. Barkov beat Rask five-hole with a shot from the right circle. Barkov's 16th goal of the season was his ninth point in nine games. Jagr's assist broke his tie with Francis.
Boston lost 3-0 at the Washington Capitals on Wednesday and arrived here about 3 a.m., but the Bruins looked energized early. They outshot the Panthers 7-0 in the opening six minutes, and eventually 10-2.
"We had a great start, the start we were looking for," Kelly said. "We're pretty disappointed with the way we played in that third period."
Julien said he sensed mental fatigue by the start of the third period.
"That's where you've got to be strong," Julien said. "At this stage, we can use all the excuses we want, but we've got to be able to get through these kinds of games, and we didn't.
"There's a lot of guys in there that are putting everything on the line, but it's not everybody."
Luongo was honored on the ice before the game -- his wife, daughter and son joined him -- for winning his 400th NHL game last week. A video montage of Luongo was shown on the arena's scoreboard and he was given an engraved, commemorative silver stick. The 36-year-old is the active leader among NHL goalies in games played (863), wins (400), shutouts (68) and saves (23,457).
Luongo made 34 saves.
"It's not sweet because we're still not in the playoffs,'' Luongo said. "But they did it to us last week (a 3-2 Boston win March 31). It was a heartbreaker so it was nice to return the favor. But we're still on the outside looking in. We'll take it and get ready for the last one and move on.''