The Islanders broke their own brooms before they could complete the sweep.

Costly penalties and undisciplined play from the Islanders led to a 3-2 loss in Game 3 of the best-of-five series with the Florida Panthers on Wednesday afternoon at Scotiabank Arena, preventing the Isles from completing the sweep. Game 4 is on Friday at noon.

An early third-period penalty on goaltender Semyon Varlamov knocked the Islanders off their game and opened the floodgates for the Panthers, who registered two third-period goals to keep their season alive.

“They got two quick goals to start the period, obviously it was a turning point,” coach Barry Trotz said on a Zoom call following the loss. “They were able to capitalize on some momentum there. One-one game, they were going to come with their absolute best effort and unfortunately, the puck bounced on Varly and he played it in the trapezoid zone and we weren’t able to kill the penalty. That’s on us.”

Varlamov was called for a delay-of-game penalty just seven seconds into the third after he mishandled the puck. Panthers forward Mike Hoffman made it count and sent a one-timer from the right circle to give the Panthers the lead 41 seconds into the final 20 minutes.

Just over two minutes later, Brian Boyle buried the puck from the slot to further suppress the Islanders’ momentum. The Panthers’ quick two goals shocked the Islanders right out of the rhythm they’ve kept since their exhibition win over the Rangers last week.

The Islanders pulled Varlamov, who finished the game with 19 saves, for an extra skater with 2:37 left in regulation and Brock Nelson capitalized, sending a centering pass in front of Panthers goaltender Sergei Bobrovsky that deflected in off a Panthers skater. But it wasn’t enough.

“A lot of the stuff they got, we can clean that up, that’s in our control,” Trotz said. “We’re going to have to clean that up. It’s a bit of a missed opportunity for us to knock them out. They’re a good hockey team, they’re a very talented team and well-coached. They have some star power.

“We got away a little bit from our game, we’ll have to get back to our game.”

The Panthers dialed up the physicality and intensity early, but the Islanders remained steady — like they have all series long — bearing down and leaning on their defensive prowess to escape the first with the game still scoreless.

Bobrovsky looked like a two-time Vezina Trophy winner as he made big-time stops on a breakaway from Jordan Eberle and an end-of-the-period frenzy from Nelson and Anthony Beauvillier.

Mathew Barzal had his best opportunity of the series early in the second, taking a hard shot on a feed from Anders Lee before Panthers defenseman MacKenzie Weegar got his body in front of it. The Islanders were then deflated by a too-many-men call that led to an Erik Haula power-play goal at 4:02 of the second to give Florida a 1-0 lead.

Not too long after, Ryan Pulock rung the post with a shot from the top of the zone that ignited a surge of dangerous plays for the Islanders. Maintaining puck possession in the Panthers’ zone for nearly two minutes, shots from Nelson, Beauvillier, Nick Leddy and Matt Martin were either blocked or saved by Bobrovsky.

A tremendous effort from Beauvillier deep in the Panthers’ zone paid off as he connected with a crashing Jean-Gabriel Pageau for the game-tying tally at 16:26 of the second.

But the Panthers capitalized on every mistake the Islanders made for the rest of the game.

“Obviously we didn’t execute our game plan and the discipline in our game plan, we didn’t do it,” Pageau said following the loss. “It’s unfortunate, but we were in a good position and we’re still in a good position, now we just got to focus again.

“We knew they were going to come out and play hard, now we’re going to have to play with urgency next game.”