When Steven Souza Jr. sprinted out of Washington’s dugout to take his spot in left field to start the ninth inning Sunday, he was the 17th and final Nationals player to enter the game against the Miami Marlins.

Sunday, the final day of a grueling 162-game regular season, was supposed to be easy. Most regulars took two at-bats and then left to loud ovations.

But Jordan Zimmermann’s near-perfection on the mound changed the day’s dynamics. Late-game substitutions had to be made with defense in mind. As Zimmermann pitched his way to the first no-hitter in Nationals history with a 1-0 win, the defense behind him — changing nearly every inning — made every play, including Souza’s diving catch in the left-center field gap for the final out.

The defensive alignment in the final inning? Rookies Souza and Michael A. Taylor in left and center , respectively, and veteran Nate Schierholtz in right. The infield was made up of utility man Kevin Frandsen at third, defensive wizard Danny Espinosa at shortstop, infielder-outfielder Jeff Kobernus at second and Tyler Moore at first. Five of those players spent time at Class AAA Syracuse this season. The lone regular position player on the field was catcher Wilson Ramos.

“All these guys can play at any given time,” Zimmermann said. “They were all ready today. We got some of those guys out of there early and brought some of those other guys in, and they were playing great all day. It’s a complete team win.”

The Post Sports Live crew makes a case for Nationals manager Matt Williams to win manager of the year for the National League after leading the team back to the playoffs. (Post Sports Live/The Washington Post)

The Nationals began the game with all of their regular players in the lineup except for Jayson Werth, who was available off the bench; Bryce Harper started in right field instead.

The Nationals had nothing left to play for in the regular season, and Manager Matt Williams’s substitutions began in the third inning with Schierholtz replacing Denard Span.

Once Span’s double — his 184th hit of the season — set a Nationals’ single-season record, Williams had Schierholtz run for him. Harper shifted to center field the next inning, and Schierholtz took over in right.

Frandsen also replaced Anthony Rendon at third base.

“It’s important to give guys rest and get them in there to have a couple at-bats to get their momentum going and their routine going and also to get them out of the game,” Williams said.

“Lots of moves and lots of trying to take care of guys at the same time and some tense moments when it finally came down to it.”

By the fifth inning, Scott Hairston — used primarily as a pinch hitter this season and on a few occasions in left field — was in right field for the first time all season.

By the sixth, left fielder Ryan Zimmerman and Ramos were the only regulars left. In the eighth, Williams put Taylor, considered the best defensive center field prospect in the Nationals’ minor league system, in the game. He removed Hairston and shifted Schierholtz back to right. For the ninth, he sent Souza to left to replace Zimmerman, a novice outfielder.

“It definitely got your blood pumping pretty quick to go in a game and have to make every play out there,” Taylor said. “It was pretty fun to be a part of it.”

Even when the Marlins hit Zimmermann’s pitches the hardest, the makeshift infield had an answer.

In the fifth inning, Zimmermann gave up three hard line drives. Moore snared the first, and Frandsen grabbed the second with quick reflexes, reaching to his right for a backhanded catch. After Justin Bour walked, J.T. Realmuto hit a ball right at Espinosa.

“That really is a total team effort right there,”’ Frandsen said. “Because look at all the guys contributing. Coming off the bench, I think pretty much [everyone] had a play that did something right there. It’s pretty cool. That gives us great momentum going into the postseason.”

The only other time Zimmermann allowed a base runner, the Nationals erased the runner with a heads-up defensive play. With two outs in the seventh inning, Zimmermann struck out Garrett Jones on a low curveball. But Ramos couldn’t corral the wild pitch — it hit him in the forearm — and Jones took first base.

Zimmermann had to face Reed Johnson with a runner on, and Johnson entered the game 5 for 9 against him in his career. Ramos knew Jones wasn’t going to steal, but Jones took too big of a lead after Zimmermann’s first pitch to Johnson. So Ramos called for another slider, a swing-and-miss pitch, and had a feeling Jones would be too far off the base again.

Johnson swung through the slider, Ramos caught it and jumped up to fire a throw to first. Moore put his left foot in between Jones and the base and tagged him out to end the inning.

“That guy gave me a chance to take him out, and I did it,” Ramos said. “That was a great play in the right moment. We need to think before it happens. I think I got a chance, so I want to prepare for that. I prepared and I did it.”

Even though Zimmermann guided the Nationals and Souza provided the memorable last out, nearly the entire team supported the effort.

“We’re deep, man,” Span said. “. . . It just speaks volumes of this organization and how they’re developing players.”