The sound of the baseball jumping off the bat of Marlins slugger Giancarlo Stanton was loud, crisp and emphatic.

Surely everyone at Citi Field knew where this second-inning blast was headed, toward the seats in left-centerfield, well beyond the outfield wall. These are the type of home runs that scouts commonly refer to as no-doubters.

But, truth be told, Steven Matz still turned to watch the ball’s flight and see where it landed. The dejected look on his face told the story. This was anything but good.

Matz’s next move was to walk off the mound, head down, his 2016 season debut finished after recording only five outs. To call this abbreviated outing a far cry from everyone’s expectations — Matz’s included — is an understatement.

The Long Island lefthander allowed seven runs in 1 2⁄3 innings as the Mets fell to the Marlins, 10-3, Monday night before 24,320 for their third straight loss. They are 2-4.

All seven of the Marlins runs that Matz allowed were scored during a second inning in which he threw 40 pitches — nearly half of the soft pitch count of 90 that the Mets had in mind. And that wasn’t even enough to get him and his team out of the inning.

Mets manager Terry Collins spoke before the game about his hope that Matz “gets back in the flow of pitching,” noting that “it’s been a while since he’s been out there.” But clearly this was a night where very few things went according to the Mets’ plan.

The shocking part of Matz’s first major-league loss was just how quickly things went south for the Ward Melville High School product.

Pitching for the first time since an exhibition game in Las Vegas on April 1, Matz breezed through the first inning. He was not affected by the umpires reversing a third-out call at first base on replay, which put a runner on with the always dangerous Stanton at bat.

Instead Matz rebounded by striking out Stanton, breezing a 2-and-2 sinker clocked at 94 mph past the Marlins slugger.

Considering all the optimism that’s surrounding the 25-year-old’s first full season at Citi Field — he was 4-0 with a 2.27 ERA in six starts last season — Stanton’s swing-and-miss had the look and feel that this would be Matz’s night.

But it proved to be the only highlight.

Matz began the second inning by issuing a four-pitch walk to Martin Prado, and the Mets pitcher never truly recovered.

After another walk to Chris Johnson and a single by J.T. Realmuto loaded the bases, Adeiny Hechavarria hit a hard grounder down the third-base line that ricocheted off the bag into leftfield, allowing the first two Marlins runs to score.

A sacrifice bunt by the opposing pitcher Jarred Cosart put runners on second and third and Dee Gordon’s infield single to second baseman Todd Walker plated another run to extend the Marlins’ lead to 3-0.

Matz had a chance to end the damage there.

Gordon stole second to put runners on second and third, but Matz got Marcell Ozuna to pop out for the second out. But then things unraveled.

Matz hung a 2-and-2 curveball to Christian Yelich that the Marlins leftfielder lined to centerfield for a two-run single. Stanton followed with his moonshot over the left-centerfield wall, and by then Collins had seen enough.

Matz was coming off an uneven spring training in which he expressed frustration at times over his struggles to get outs. But he pitched better late in camp, which Collins attributed to Matz not overthrowing his fastball and improving the quality of his secondary pitches.

Collins hoped to see Matz build off that Monday night. Now the manager has to hope his young pitcher has a short memory.