If the Mets intend to avoid becoming inconsequential specs in the rearview mirror, they can’t give away chances to gain ground. In their current depleted state, they simply aren’t good enough to make careless mistakes.

Which is why the Mets’ 4-3 loss to the cellar-dwelling Braves on Saturday night offered a star reminder of just how precarious a season of promise has become.

The Mets blew a 3-0 lead, with the winning run crossing the plate in the eighth inning, aided by an inexplicably half-hearted throw by Curtis Granderson and a pitch in the dirt that catcher Rene Rivera couldn’t track down in time.

Ender Inciarte took advantage. He was standing on second base — representing the go-ahead run — when Jeff Francouer hit a liner to Granderson in right for the first out of the inning. But Granderson took his time throwing the ball to the infield. And when he did, he made only a half-hearted toss. Noticing the opening, Inciarte bolted for third.

Inciarte completed his trip when Addison Reed bounced a pitch in the dirt, forcing Rivera to scramble for it. Once he retrieved the ball, it became a footrace to the plate. Inciarte won that contest, too.

He emerged from a cloud of dirt, his face revealing an adrenaline-fueled dash around the bases that left the Mets stunned.

Those faces were contorted again in the ninth, when the Mets blew their chance at a walk-off victory, this time because of an overaggressive send by third-base coach Tim Teufel.

After Wilmer Flores reached on an error by shortstop Erick Aybar, James Loney laced a double to the gap in left-center. The Mets would have easily had runners on second and third with nobody out.

But Teufel waved around Flores, the slowest position player on the team. After a relay, Flores was cut down at the plate. In the coach’s box, Teufel slumped his shoulders and kicked the grass, his folly immediately clear.

Loney advanced to third base on a wild pitch and Alejandro De Aza got plunked. But with the winning run on base, Granderson struck out looking.

With the loss, the Mets fell 6 1⁄2 games behind the front-running Nationals, the biggest gap they have faced all season. That number can only grow to seven games if the Nationals prevail Saturday against the Padres in San Diego.

And, of course, the Mets couldn’t go another night without another injury scare.

Jim Henderson left the game in the seventh inning, two batters after allowing a game-tying solo shot to Tyler Flowers in the seventh inning.

Henderson walked off the mound during a visit by pitching coach Dan Warthen. The pitcher made a beeline to manager Terry Collins and trainer Ray Ramirez in the dugout — an ominous sign after the radar gun indicated there might be an issue.

Though his fastball velocity has averaged 93.6 mph this season — after spending all last year coming back from his second shoulder surgery — Henderson averaged just 91 mph with his fastball Saturday. He had recently dealt with an issue with the fingernail on his right hand, which affected his availability last weekend in Milwaukee.

The Mets did not immediately reveal the nature of Henderson’s apparent health issue. Indeed, the Mets can ill afford yet another long-term injury. Henderson entered the game with a 3.96 ERA in 30 appearances, though his performance has tailed off since posting a 1.08 ERA in 12 April relief outings.

Henderson’s entrance only brought on more frustration for the Mets, who had taken a 3-0 lead only to watch it slowly disappear.

Yoenis Cespedes and Flores blasted solo shots. Rivera lifted a sacrifice fly, scoring Loney after he stretched a sure double into a daring triple.

The Braves chipped away at Long Island’s Steven Matz, who allowed two runs and four hits in six innings. He allowed a solo shot to Francouer and an RBI single to Chase d’Arnaud. Nevertheless, Matz left with the Mets ahead 3-2, in line for his first victory since May 25.

It took just one pitch for those hopes to evaporate.

Flowers homered on Henderson’s 91-mph fastball. With that, Matz was assured his winless streak would grow to four games, all after winning seven straight decisions.