The gap between the Yankees and Mets has seldom been wider in the interleague era.

In case there was any question about the breadth of the chasm, the Yankees grated Steven Matz’s face into the dirt Thursday, completing the second season-sweep of their crosstown rival in the 21-year history of the Subway Series with a 7-5 victory at Citi Field.

“It sucks to suck,” Matz said, referring to his recent body of work. “I know that.”

But he might as well have been referring to his entire team.

We can now resume the regular machinations of the New York baseball season, with the Yankees competing for the playoffs and the Mets just trying to figure out which players fit for 2018.

Gary Sanchez brought the thunder, matching a career high with five RBIs, bludgeoning Matz and carrying the Yankees to a fourth straight victory in the series. The dreadful 2003 Mets of the Art Howe era were the only other Mets team to get swept in the Subway season series; the Yankees went 6-0 that year.

“The most important thing is getting the wins,” Yankees manager Joe Girardi said, downplaying the significance of Subway bragging rights. “Especially this time of year.”

And now the party moves to Boston, where the Yankees will face the Red Sox for three games with aspirations of turning the AL East into a dogfight. The Yankees will begin play four games behind the Red Sox.

Luis Severino (10-5) gave the Yankees their best pitching performance of the 2017 Subway Series, limiting the Mets to one unearned run on four hits over 6 ¹/₃ innings. It was a rebound performance for the right-hander, who had an abysmal outing against the Red Sox last weekend, when he surrendered 10 runs — eight of which were earned — in 4 ¹/₃ innings.

“I was ahead on the count almost all the time,” Severino said. “I think the last time I tried to pitch around the batters. This time I went after them.”

Curtis Granderson hit a grand slam — the seventh of his career — against Bryan Mitchell in the ninth to make it briefly interesting before Dellin Betances got the final three outs for the save.

“It’s not really want you want to do,” Girardi said of using Betances, noting he would be unavailable Friday. “But we had to win the game, so I had to go to him.”

Sanchez hit a three-run homer in the first inning to start the runaway and delivered two additional runs with a single in the fourth against Chasen Bradford.

Matz (2-7) was putrid, allowing seven runs, six of which were earned, on seven hits and two walks with four strikeouts over 3 ¹/₃ innings. The lefty fell to 0-6 with a 10.19 ERA over his last eight starts.

“I have been trying a bunch of different stuff and it just hasn’t been translating,” Matz said. “With guys on, that is where I am getting hurt.”

Manager Terry Collins suggested Matz’s next turn in the rotation could be skipped. Collins was asked what has been different about Matz lately.

“The one glaring difference is he doesn’t throw as many sliders as he once did because of the wear and tear on his arm,” Collins said.

The Yankees set the tone for the night when the game’s leadoff hitter, Brett Gardner, his a bouncer that Matz fielded and threw away for a two-base error. After Aaron Hicks walked, Sanchez cleared the left-field fence for his 22nd homer of the season.

In the fourth, Severino was credited with his first major league hit after Dominic Smith couldn’t handle his popped-up bunt, loading the bases. Gardner delivered two runs with a double before Aaron Judge was hit by a pitch and Sanchez greeted Bradford with a two-run single.

The Mets scored an unearned run in the seventh on Matt Reynolds’ RBI single after Judge dropped Travis d’Arnaud’s fly ball for a two-base error.