The Nets defense went missing in the first quarter, and they were missing shots in the fourth.

But it was losing their poise at the end that cost them.

The Nets blew a lead down the stretch in a 107-99 loss Monday night to the tanking Wizards before a sparse gathering of 13,785 at Capital One Arena, their second defeat in a month at the hands of the worst team in basketball.

Yes, the Nets trailed by 14 points less than five minutes in.

But they had a 95-92 edge with 5:39 to play only to allow a 15-4 Wizards run to close the game.

“We lost our composure and we were not good with whatever happened with a flagrant and a technical and all that stuff and a foul before the ball gets inbounded,” coach Jordi Fernández admitted. “Those [hurt]. All those things are a lack of focus, and that’s not the team we want to be. Obviously you want to be focused, and you want to play really hard and support your teammates and fight for your teammates. But that’s not who we want to be.”

Brooklyn big man Nic Claxton picked up another flagrant foul for a push in the back during the fourth quarter.

Trendon Watford committed a foul before an inbounds, and also got hit with a technical down 103-99 with 13 seconds left in the game.

After the Nets had taken a 95-92 lead on Keon Johnson’s pull-up 3-pointer with 6:05 left, they imploded. Brooklyn (21-36) missed seven of their final eight shots and had a couple of turnovers.

The Nets came in having won seven of nine, but got outhustled by a team that’s just 10-47 and had lost six straight.

“We didn’t defend the whole game. For the whole game, our focus was bad,” Fernández said. “Our purpose, focus, everything we’ve had going well for us the last three games … I just couldn’t see it [Monday]. We’ve got to be better, starting with me.”

The loss dropped the Nets 1 ½ game behind Chicago for the final play-in spot, but kept them one below the 76ers for the sixth spot in the draft lottery standings.

Ziaire Williams had 19 points, three steals and was a career-high 5-for-7 from deep.

Cam Johnson added 17.

But the Nets were abysmal to start, allowing Washington to hit seven of its first eight shots.

Richaun Holmes’ dunk put the Nets in a 21-7 hole just 4:59 into the game, with Fernández yanking his entire starting lineup off the floor.

Down 67-59 at the break, the Nets scored the first seven points of the second half to get within one.

They mounted a 20-7 run later in the third to seize the lead, a Williams 3-pointer putting them up 81-74.

But after the Nets gave up a 14-4 run that spanned the third and fourth quarters, the final stanza was feisty.

Martin and Khris Middleton got into it after the Washington guard missed a 3-pointer in front of Brooklyn’s bench.

The Nets were clinging to a 95-92 edge, but gave up a 14-4 run to end the game.

Claxton now has six flagrant points this season, so will be looking at a one-game suspension unless his Flagrant 1 gets overturned by the league office.