Tampa Bay’s Brian Lee provides a welcome assist for prone goaltender Mathieu Garon as Jay Beagle attempts a wraparound shot in the first period. (Mike Carlson/ASSOCIATED PRESS)

By the midway point of the third period at the Tampa Bay Times Forum on Thursday night, the Washington Capitals had built a commanding three-goal lead. As time ticked down, though, they would need every last bit of that advantage to fend off the explosive offense of the Tampa Bay Lightning.

Tampa Bay scored a pair of goals in the final 7 minutes 58 seconds as the Capitals took their foot off the gas pedal. Washington made careless mistakes like failing to get the puck deep or losing track of assignments defensively, and after a strong start Braden Holtby suddenly looked fallible.

Despite the Lightning’s efforts, Holtby, who finished with 27 saves, and Washington held on for a 4-3 victory. While the Capitals were glad to extend their winning streak to three games, they could have made it a much less anxiety-ridden task than it was at the end.

“We’ve got to clean it up a little bit,” said Troy Brouwer, who recorded his team-high seventh goal. “We made a few mistakes. We’ve tried to fall back on our systems and make sure that we’re doing the right things, but giving up a 4-1 lead and making it a game isn’t what we need right now. We thought we had them. Maybe that’s the reason why they were able to come back is because we let up a little bit.”

The Capitals started off well enough. Holtby was making timely and tough saves to fend off the desperate Lightning, which hasn’t won since Feb. 1, and the offense was clicking with goals and extended possession time.

The Post Sports Live crew examine the scrutiny on Capitals general manager George McPhee and debate whether he is the man most responsible for the team’s slow start to this season. (Post Sports Live/The Washington Post)

Brouwer scored 2:40 into the first from the slot on a tic-tac-toe power-play sequence to make it 1-0, marking the sixth straight game Washington capitalized on the man advantage. Martin St. Louis tied it at 8:23 after getting several stuff attempts before he beat Holtby.

In just their third game together as a unit, the Capitals’ third line of Eric Fehr, Mathieu Perreault and Joel Ward grabbed the spotlight once again. Just more than five minutes into the second, Fehr scored to make it 2-1 after Ward hustled to beat a flat-footed Matt Carle to the puck behind the Lightning net and threw it in front. The puck deflected off Perreault’s skate and over to the winger on the right side of the net.

“I definitely want to help contribute,” said Fehr, who scored goals in consecutive games for the first time since October 2011. “I think we work really well together. We have a little bit of everything. We protect the puck well, we cycle well and we work hard. In this system that’s all you need to go.”

Fehr added his second goal of the night 2:22 into the third on a booming slap shot for a 3-1 lead and his first two-goal game since March 9, 2011, during his first stint with the Capitals. A little more than five minutes later on a strong, net-crashing shift by the fourth line, Jay Beagle recorded his first goal of the season and the eventual game-winner. He fished the puck out from underneath Tampa Bay netminder Mathieu Garon (35 saves) and swatted it into the net for a 4-1 advantage that seemed comfortable.

Problem was, the Capitals got a little too comfortable with it.

“We knew they were going to make a push. They’ve got the skill to do it and they got a couple goals at the end we could’ve easily avoid,” said Perreault, who recorded his first-career three assist game. “I feel like we might’ve sat back a little bit too much and when we do that, we seem to always get a couple goals against, so I feel like we shouldn’t be sitting back that much.”

Teddy Purcell scored on a bad-angle shot with 7:58 remaining in regulation to cut the deficit to 4-2. Less than five minutes later, a turnover by Ward deep in the offensive zone sprung Nate Thompson on a breakaway. Holtby tried to poke-check the puck away but missed, resulting in an easy goal for Thompson that made it 4-3 with 3:13 left in regulation.

“Once I saw him lose it, I thought I’d be able to get out there and get it before he did, but I read it wrong and that’s a bad mistake,” Holtby said. “Luckily it didn’t cost us, luckily we battled back, but that can’t happen.”