June 22, 2021 | 12:10am | Updated June 22, 2021 | 12:10am

So that’s what a clutch two-out hit by the Mets looks like, in case it had been so long that you forgot.

As much as this Jacob deGrom start felt different than others before it — because of the new umpire inspections for sticky substances and the ace’s recent early exits caused by elbow and shoulder pain — it was following a familiar script until Dom Smith stepped to plate in the bottom of the fifth inning. DeGrom was dominant with little breathing room created by big hits.

Then Smith lined the sixth pitch of an at-bat into the right-field corner for a two-out bases-clearing three-run double that provided the necessary insurance Monday in a 4-2 victory over the Braves in the opener of a doubleheader at Citi Field.

The rally came out of nowhere and manifested on three consecutive pitches. Tomas Nido was plunked by an 0-2 sinker ahead of back-to-back first-pitch singles by Jeff McNeil and Jonathan Villar. Fresh off the injured list, McNeil pinch hit for deGrom — who threw 70 pitches in five shutout innings — and wasted no time in his first at-bat since May 16.

Francisco Lindor, who single-handedly kept the Mets from a four-game sweep against the Nationals with a two-home run and five-RBI game, couldn’t stay hot. He bailed out reliever Shane Greene with a lazy fly out to right on a 3-0 pitch.

Dominic Smith wouldn't let Jacob deGrom's gem be wasted
Dominic Smith wouldn’t let Jacob deGrom’s gem be wasted.
Charles Wenzelberg/New York Post

That put the weight of a weak week on Smith in a lefty-on-lefty matchup against Sean Newcomb.

“It’s definitely huge,” deGrom said. “Lindor put a good swing on that ball and he just missed it. You want to pick each other up and Dom did a great job of that, so everybody was excited to tack on another three runs there.”

The Mets were hitting .163, including .095 with runners in scoring position, with a .525 OPS over the past five games entering the doubleheader. No wonder then that the Mets were averaging 1.8 runs per game in that span.

One swing doubled that output as the ball two-hopped the wall and Smith jogged into second base with both hands extended toward the sky as he looked back at a relieved dugout.

Smith, who nearly sparked another rally before the Mets dropped the nightcap, 1-0, saw his monthly OPS has risen each month this season, from .549 in April to .706 in May to over .800 in June. But Game 1 of the doubleheader was only his second multi-RBI game since June 2, not up to the No. 3 hole standard.

Smith continued to beat up left-handed pitching, increasing his average to .304. But Braves manager Brian Snitker ignored those percentages and played the handbook by removing Greene despite Smith’s .227 average — with five home runs compared to one off lefties — against righties.

Just how important was Smith’s clutch hit?

DeGrom’s mastery would have been wasted without it because the Braves started the sixth with a walk and a two-run home run.