PITTSBURGH — Things seldom have gone downhill for this Lightning team as quickly as they did Sunday night against the Penguins at PPG Paints Arena.

Even on its worst nights, it is a group that finds ways to stop a slide. But on the road against a desperate team fighting for a playoff spot, the second-period buzzer was the only thing that finally halted a Pittsburgh onslaught.

The Lightning allowed five straight goals over the final 4:32 of the second period and suffered one of their worst trouncings of the season, 7-3.

“It doesn’t happen very often when you give up, whatever it was, four or five goals in that span,” captain Steven Stamkos said. “So (the Penguins) carried some momentum, and we just fell behind. I don’t know if it was fatigue or just mental lapses, but it’s just one of those nights where it was tough.”

Over the past three contests, including games in Detroit and Pittsburgh the past two nights, Tampa Bay (37-18-4) has played too loose in its end. Whether it was too many odd-man rushes in an overtime loss to Buffalo on Thursday or open looks in front of the net Saturday in a win in Detroit or the unsightly combination of both against Pittsburgh, the Lightning have seen better days defensively.

“It’s happened a couple times as of late,” defenseman Mikhail Sergachev said. “So we’ve got to look ourselves in the mirror and learn something from it. And we’ll obviously do it, because our group is tight and everybody’s a professional and we’ve got a great group of veterans to take care of the group and the coaches, obviously, so I’m 100% sure we’re fine.”

The collapse soured a record-setting night for forward Nikita Kucherov, who, with a first-period goal, became the quickest Lightning player to 700 career points, reaching the milestone in 621 games, 75 fewer than Stamkos.

The Lightning took a 2-1 lead on Kucherov’s goal into the second period, but Evgeni Malkin’s tying goal 6:17 into the period seemed to take the steam out of them. As Malkin exited the penalty box, he received forward Josh Archibald’s stretch pass between Lightning forward Ross Colton and Sergachev, giving him an easy breakaway.

Officially, it was an even-strength goal, but it was the latest defensive lapse by a power play that has given up 10 shorthanded goals this season.

“Special teams are part of the game, and you’re not always going to score on your power play,” coach Jon Cooper said. “But you want it to give you a little bit of momentum, and it probably took a little away from us.

“It’s not going to count as a shorthanded goal, but it might as well have been, and that’s been a bit of an Achilles’ heel for us throughout the year.”

After Stamkos went to the box for hooking, Sidney Crosby was left open at the back post for an easy power-play goal with 4:32 left in the period to make it 3-2. Pittsburgh fourth-line center Teddy Blueger then was the first player to the front of the net after a hard puck carom off the end wall, making it 4-2.

“We just made some plays we weren’t making when we were playing well,” Cooper said. “We were turning pucks over — a multitude of guys were doing it — and then we were losing some battles down low. And I think the harder we tried, the worse it got, if that makes any sense.

“Everybody was trying to make up for mistakes and cover guys, and if we had just taken a breath and relaxed, we would have been fine.”

Penguins forward Jeff Carter had an open shot from the right circle after four Lightning players drifted to the opposite corner in a battle for the puck, and he made it 5-2 with 2:10 left in the second. Shortly afterward, Tampa Bay again was caught with four players on one side of the ice, and Malkin fed forward Jason Zucker in front to make it 6-2. Defenseman Brian Dumoulin added a goal with 4.2 seconds remaining in the period.

Lightning forward Brayden Point ended Pittsburgh’s string of goals with a power-play goal just under 8 minutes into the third period for his team-high 36th of the season.

“When it started unravel in those last five (minutes of the second period), I thought maybe we were feeling sorry for ourselves a little bit, and that’s not been part of this team for a long time,” Cooper said. “That’s something we don’t do, so probably a little mental correction there for us.

“But we haven’t really been a part of that before, so hopefully it’s a one-off.”

The Lightning are just one game above .500 (15-14-1) on the road this season while posting a minus-10 goal differential and allowing 3.3 goals per game away from Amalie Arena.

“For me, we’ve got to get better on the road,” Cooper said. “In the end, that’s what we have to do. At home, we’ve been able to hold our own, but on the road, we have to dig our heels in a bit better, and that’s something we have to work on.”

Contact Eduardo A. Encina at eencina@tampabay.com. Follow @EddieintheYard.

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