BOSTON — The legacy of the 2019 Red Sox, barring a stunning revival, will be simple enough, and they could very well choose a three-batter fourth-inning sequence from Saturday afternoon at Fenway Park to illustrate the whole darn thing:

They didn’t do their part to stop the Yankees. Not last winter, and certainly not this spring and summer.

After J.A. Happ and his Yankees teammates shut down the Bosox, 5-1, they could enjoy a night out with this knowledge: Two more wins to close out this wrap-around series, this season series, and they’d officially eliminate the defending champions from American League East contention. That would constitute sweet vengeance, if not the ultimate justice — the Sawx possess more rope, albeit thin, when it comes to qualifying for the postseason as a wild-card entry — against the rivals who ousted them in last year’s AL Division Series.

“Let’s finish this series now, and we’ll see,” said Red Sox manager Alex Cora, who then helpfully mentioned Brett Gardner’s memorable Yankee Stadium grand slam on April 17 and the Yankees’ two-game London sweep before concluding, “We’ll see what happens here, and then we can talk about that.”

With all due respect to Cora, I’d like to discuss it right now. The Yankees, whose magic number to clinch the division stood at 11 entering Saturday night’s Blue Jays-Rays game (it was 10 to make the playoffs, the Indians-Twins contest serving as the key determinant there) own a 12-5 record against the Red Sox. Their best showing versus Boston since the return of the unbalanced schedule in 2001 has been 13-5, in both 2001 and 2012.

For as much grief as the Yankees received from their fans last winter for their Hot Stove decisions — it sure looks like they should’ve spent on Patrick Corbin, whereas they’ve gotten by pretty well without Bryce Harper and Manny Machado — the Red Sox evaded similar offseason scrutiny thanks to their parade and trophy tour after defeating the Dodgers for their fourth Fall Classic title in 15 seasons.

Yet they essentially re-signed Nathan Eovaldi and Steve Pearce and called it a day, and they are paying the price for such a laissez-faire approach to team-building, their 76-66 record leaving them on the periphery of the top-heavy AL race.

Their pitchers, clearly hungover after last year’s arduous workload, have largely broken down and been diminished, and the Bosox brought 24 active pitchers into the weekend, bullpenning in the series’ first two games.

Then you had a day like Saturday, which would lead even the most ardent baseball atheist to believe in karma.

The game stood scoreless, Boston’s conga line of relievers doing its job for a second straight day, when Didi Gregorius came to bat with one out and a runner on first base in the top of the fourth inning. Gregorius barreled a ball to right field that regular designated hitter J.D. Martinez lost in the late-afternoon sun. The ball tipped Martinez’s glove and went behind him, and Gregorius enjoyed a double, with DJ LeMahieu advancing to third.

“Terrible,” Martinez said of the sun. “I would say this place, 4 o’clock games, [is] one of the worst I’ve seen. … You pray for clouds, pretty much.”

The very next batter, Gary Sanchez, lofted a flare to short right field. Martinez pursued it, and second baseman Brock Holt went after it with even more gusto. Neither could snare it, and the ball landed a couple of feet in fair territory and bounced into the stands, giving Sanchez an unlikely two-run, ground-rule double, ending the scoreless tie.

“As an outfielder, you’ve got to take charge of that one,” said Cora, a former infielder.

“If I could go back in time, I would’ve said, ‘I got it, I got it, I got it!’ ” Martinez agreed.

The next batter, Edwin Encarnacion, destroyed a curveball from Colten Brewer well over the Green Monster, onto Lansdowne Street. Just like that, the Yankees owned a 4-0 lead that never faced any serious jeopardy. Not unlike the Yankees’ divisional lead over the Sawx.

“I feel like we haven’t been playing bad,” Martinez said, “but we haven’t been ‘hot hot.’ ”

Particularly against the Yankees, who surely regard taking care of business up here as a pretty cool thing.