LANDOVER, Md. — Ain’t that a kick in the head.

The Giants somehow found a way to lose a game they had no business losing, mainly because they did not have a kicker and the Commanders did.

In what must go down as a low moment for a franchise that recently has experienced a whole bunch of them, the Giants walked off the field at Northwest Stadium on Sunday on the very wrong end of a 21-18 loss that was absurd and embarrassing.

They were done for when Austin Seibert, signed this week, nailed his seventh field goal of the day, from 30 yards out as time expired.

Cue coach Brian Daboll, who ripped his headset off his head and slammed it to the ground.

The Giants did not give up a touchdown to rookie quarterback Jayden Daniels but they also could not get the Commanders off the field all day.

The Giants became the first team in NFL history to score three touchdowns, allow no touchdowns and lose in regulation.

The Giants refused to attempt a field goal because they lost their kicker, Graham Gano, to a hamstring injury on the opening kickoff.

Gano came into the game with a sore groin and yet the Giants did not elevate Jude McAtamney off the practice squad.

“I’m sure whatever decisions our staff makes are the right ones,” Gano said. “I’m sure if we could do it again we’d do the exact same thing.”

Um, well, perhaps not.

“We thought Graham would be OK,’’ Daboll said. “He got hurt chasing. It was a hamstring. He didn’t hurt his groin. He hurt his hamstring.”

The entire tenor of the game was knocked off course on the opening kickoff, when Gano sent the ball to the 2-yard line and Austin Ekeler returned it 98 yards for a touchdown.

Gano gave chase down the sideline and pulled up, clearly hurting his right hamstring.

Gano, 37, could not have known that a yellow penalty flag was thrown far up the field and the return would not stand.

Gano insisted the new hamstring injury was in no way related to the groin issue.

“It was just tough luck,” Gano said. “It wasn’t something that was bothering me at all until I guess I was running too fast for my body.”

That decision proved to be fatal as the Giants dropped to 0-2.

They squandered five points (two failed two-point conversions, one missed extra point) because they did not have a backup kicker capable of actually kicking.

After Devin Singletary scored on a 7-yard run to put the Giants ahead 6-3 late in the first quarter, Daboll called on punter Jamie Gillan for the extra point — the first one of his four-year NFL career.

Gillan’s line drive kick sailed wide right and that must have spooked Daboll.

When Jones hit rookie Malik Nabers on a 4-yard touchdown strike with eight seconds left in the first half, the Giants were ahead 12-9 and Daboll called for a two-point conversion try.

It failed when Daniel Jones’ pass intended for Darius Slayton failed to connect.

It really got absurd early in the fourth quarter, when Jones hit Wan’Dale Robinson for a 7-yard scoring pass play to put the Giants ahead 18-15.

Daboll again called for the two-point attempt and this time Jones’ throw glanced off Slayton’s hands.

“He missed the first one and we thought our chances were better going for it or going for two as the game went on,” Daboll said.

It got really, really even more absurd in the closing minutes.

It was 18-18 and Jones was cooking, hitting Slayton for 13 yards and Nabers on a crosser for 29 to the Washington 28 — already in range for a game-winning field goal.

On fourth-and-4 from the Washington 22, Daboll again showed no faith in Gillan, who hit a 40-yard field goal last season against the Saints.

Jones rolled to his right and drilled the ball to Nabers, who made sure his feet were inbounds on the right sideline.

The Giants had the first down but Nabers slid and dropped the ball.

He pounded the turf in disgust with 2:04 left in regulation.

“I’m disappointed,” Nabers said. “No matter how good of a game you can play, that last play came down to me. I’m hurt that I let those veterans down. That’s the main model that’s in my head — don’t let my team down. And I let my team down.”

Nabers finished with 10 catches (on 18 targets) for 127 yards.

Jones shrugged off his poor opening-day struggles in a loss to the Vikings to complete 16 of 28 passes for 178 yards, two touchdowns for a passer rating of 100.00.

After the Nabers drop, once again, the defense let the Giants down.

Rookie quarterback Jayden Daniels hit wide-open Noah Brown for 34 yards and later scrambled for 14 yards, setting Seibert up for the game-winner.

“When we got somebody by the throat as a defense, we kind of got to snap their neck off and not let them get off the hook,” defensive end Brian Burns saidof a defensive unit that was gashed for 215 rushing yards.

The chances were many and the Giants failed to cash in.

They came out in the third quarter and were on the march, as an effective Singletary (16-95) ripped off a 15-yard run to the Washington 32, but cornerback Benjamin St-Juste punched the ball out, safety Jeremy Chinn recovered the fumble and the drive was cooked.

“Can’t have it,” Singletary said.

There was plenty of that going around.