Brian Daboll has shown plenty of emotion throughout training camp — after delay of game penalties, after other Giants lapses — and it didn’t take long for those reactions to materialize in the team’s preseason opener Friday night.

After the Lions’ Maurice Alexander returned a punt 95 yards for a touchdown just minutes into the third quarter, Daboll gave special teams coordinator Thomas McGaughey a glare on the sidelines.

The broadcast camera didn’t capture McGaughey recognizing Daboll’s stare, but the head coach didn’t move his eyes as McGaughey kept walking down the sideline.

“When you usually give up those long punt returns, it’s a momentum-changer,” Daboll said.

It certainly altered the Giants’ 21-16 loss on Friday, though there wasn’t much at stake besides spots on the Giants’ 53-man roster.

But when quarterback Tommy DeVito was sacked on third down, the Giants had a 10-point lead over the Lions.

That was erased after the special teams touchdown, another Giants punt and a Detroit field goal, though kicker Graham Gano briefly gave them back the lead in the fourth quarter.

Everything started when punter Jamie Gillan sent his punt down the field, forcing Alexander to backpedal and collect the ball around the 5-yard line.

Long snapper Cameron Lyons missed the first tackle.

Then, as Alexander regained his footing, cornerback Gemon Green couldn’t knock Alexander to the Ford Field turf, either.

And by the time Alexander crossed the 50-yard line, there wasn’t another Giants player who had a chance to prevent the touchdown. 

During his postgame press conference, Daboll said that the Giants had 10 guys on the field, though it’s unclear whether he was referring to the actual punt or the initial formation — when the Giants were flagged for a delay of game penalty.

The Giants appeared to have 10 players on the field during the punt that was returned for a touchdown. 

“Give them credit,” Daboll said. “It was a heck of a play.”