Pitching coach Steve McCatty and Manager Matt Williams chatted casually in the first inning about which pitchers they would use in relief of Jordan Zimmermann for the seventh, eighth and ninth innings as preparation for the start of the National League Division Series on Friday.

What else would you do on the meaningless final day of the regular season when almost everything wonderful that could happen to a team had already befallen the Washington Nationals?

Then, in the third inning, as Zimmermann, the two-time all-star right-hander, ripped through the Miami Marlins’ order — nine up, nine down — McCatty offered a different thought.

“What’ll we do if he goes six innings and hasn’t given up a hit?” McCatty asked.

“That isn’t funny,” said Williams, who wasn’t smiling at the prospect of having his plans messed up by one of those stupid no-hitters-in-progress that almost never pan out.

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)

“Well, get ready for it,” McCatty said.

No one else was ready, not even Zimmermann, for the first no-hitter thrown by a Washington pitcher since 1931.

And no one, not the craziest of the 35,085 fans at Nationals Park on the most blissful of fall days, would have dared dream how this 1-0 Washington victory would end. They never suspected that they were about to see what Williams called “all in all, probably the perfect baseball day.”

[Columnist Thomas Boswell finally sees a no-hitter live, after decades covering baseball]

In the top of the ninth inning, defensive replacement Steven Souza Jr. began practicing explosive sprints in left field, not the usual “get-loose” running of baseball. The International League MVP at Class AAA Syracuse this season knew he was part of one of the most bizarre defenses that ever tried to protect the last three outs of a no-hitter.

Inning by inning, Williams had replaced starters so they could get individual ovations — Denard Span for his 184th hit (a team record), Ian Desmond for his 24th home run. Only catcher Wilson Ramos, dialed into Zimmermann’s masterpiece like a second soul, stayed for the finish.

Nate Schierholtz, Kevin Frandsen, Tyler Moore, Danny Espinosa, Michael Taylor and Jeff Kobernus, several playing out of their normal (or best) positions, all had variations on the same thought that possessed Souza: “If it’s hit to me, it doesn’t matter how, I’m going to get it. . . . If I have to run into a wall, if I gotta break an ankle, I’m gonna catch this ball.”

With the final swing of the final day, the Marlins’ Christian Yelich lashed a high liner into the gap in left-center field. Zimmermann threw his head back in disgust. “Double. A no-doubt double,” he said he was thinking. “I don’t think anyone in the stadium expected Souza to get anywhere close to that one.”

At 6 feet 4, 230 pounds, Souza is the rare player who combines speed with football size. But that power, which produced a 440-foot home run to center field here Thursday, also means his speed is usually qualified as being merely good “for a big man.” But the Nationals watch out for him during batting practice because he’s rip-snorting around the outfield madly working on his defense. “Souza’s out there busting it every single day,” reliever Drew Storen said.

As he ran, Souza knew he was never going to get to this ball. Or he almost knew it. His memory “blacked out” afterward. He doesn’t remember the instant when he realized “maybe.” But the picture comes clear for him in the fractions of a second when he “laid out” full-length.

“I jumped at kind of a weird angle,” said Souza, who was near the warning track by the 377-foot sign. Outfielders know that, if they must, they can actually reach backward, over their heads, and still hope for a catch. Souza always wanted to try to “dive straight backwards.” But he never had. Until suddenly he did.

“My second hang [time] came on,” Souza said in the casual way that athletes understand but baffles the rest of us. Then he laughed, “And I hung on [two-handed] like a football . . . so it wouldn’t bounce out.”

Near the mound, Zimmermann threw both arms straight up. In the celebratory mob scene, he found Souza and screamed, “I love ya!” Afterward, he said, “Whatever he wants he can have.”

Souza makes the major league minimum and only for the days he spends with the big club. Zimmermann’s on a $24 million deal. “I’ll be looking for a Beemer in my garage,” Souza said. “No, I’m not looking for anything at all. Just to make that catch is enough for me.”

Some games — and some seasons — are an honor to watch. Players sense it, join in the experience of fans, almost watching themselves perform as they are in the act. “Epic day for an epic season,” Span said.

Every team says it wants to peak at the right time. But this is preposterous. The Nats have baseball’s best record since the All-Star Game (45-24) but have gotten progressively hotter, turning the dial from sauna to inferno. Since Aug. 12, excluding three games when they rested most regulars and skipped their normal rotation because wins weren’t needed, they’ve gone 33-10. That’s the real team.

This day encapsulated an entire season that began as a constant injury struggle and ended in a delicious excess of health and fun. When face-of-the-franchise Ryan Zimmerman, who has missed 101 games, came to bat in the first inning, he got a loud, unprompted chorus of “Happy (30th) Birthday to You.”

It’s hard to believe the first no-hitter by a Washington pitcher in 83 years could feel like the logical continuation of a trend, but Zimmermann’s jewel was exactly that. The Nationals’ normal five-man rotation has gone 13-0 in its last 13 starts with a 0.89 ERA. In their most recent starts, Doug Fister (complete game), Stephen Strasburg and Gio Gonzalez (career-high 12 strikeouts) allowed three, two and one hits. None allowed a run. Zimmermann added the “zero” in the hit-column progression.

“Probably good we don’t have a game tomorrow,” McCatty said. “We can’t top it.”

If this team doesn’t do well in the postseason, it’s going to give a bad name to perfect preparation. Past performance is no guarantee of future results. But it’s a pretty good place to start looking.

“We’ve had all these pieces, but they didn’t all click at once,” Storen said. “Then they did. And it’s snowballed now for months. A good snowball.”

Since the Senators’ successes of the early 1930s, Washington has had only a handful of moments to match this Zimmermann-Souza crescendo. The first game back in D.C. in 2005 surpasses it for emotion, and two division crowns exceed it for significance. Jayson Werth’s Game 4 walk-off home run two years ago in the National League Division Series still tops the lot.

But this game had an extra element — a sense of foreshadowing. On a splendid afternoon, a roaring house on South Capitol Street experienced a historic game with an indelible final moment; it felt like a fitting coda to the season but also a perfect prelude to the playoffs.

For more by Thomas Boswell, visit washingtonpost.com/boswell.