Left fielder Michael Morse pantomimes a home run swing after returning to the batter’s box following an umpire’s review of his grand slam in the first inning. (John McDonnell/The Washington Post)

The whole year had been a fantasy come to life, a magic carpet ride from the first throw of spring training to the heart-pounding thrills of early fall. As they inched closer Saturday night to their crowning moment, to popping Korbel corks and spewing Miller Lite cans, the Washington Nationals somehow found an appropriately delirious means of moving one victory away from Washington’s first first-place finish in 79 years.

In the first inning, Michael Morse stood at home plate and hit a pretend pitch with an imaginary bat for a grand slam, and they counted it for real on the actual scoreboard of Busch Stadium, a true, live major league ballpark. In the 10th inning, after their lead had slipped away, Kurt Suzuki smoked a two-run double off the left-center field fence. He clapped his hands hard on second base and looked into a raucous dugout.

Morse’s dream-come-true and Suzuki’s latest clutch hit paced the Nationals’ 6-4 victory over the St. Louis Cardinals that, in tandem with the Atlanta Braves’ win over the New York Mets, reduced the magic number for the first division title since baseball returned to the District to one. Win Sunday, Game 159, and they clinch the National League East.

“We’re ready to pop some champagne,” reliever Tyler Clippard said. “We’re itching.”

The Nationals lost control Saturday night after the Cardinals rallied for three runs in the seventh inning. They lost the lead when Drew Storen blew a save opportunity for the first time this season. Together, it turned a comfortable victory into a watch-through-your-fingers finish against an opponent pushing for the postseason — the perfect preview for October.

“To be playing do-or-die baseball for the past week or so is obviously going to get us ready,” third baseman Ryan Zimmerman said. “To have those kind of games is kind of preparing us. Not a lot of us really know what to expect. Nothing’s going to come easy, and I wouldn’t expect it to come easy.”

It sure didn’t Saturday night. The Cardinals erased what remained of the Nationals’ four-run lead in the ninth off Storen. With one out, Pete Kozma rifled a single through the left side and into left field. Pinch-hitter Daniel Descalso rolled another single into right, which put runners on the corners. Jon Jay crunched a first-pitch, 95-mph sinker deep to center field. Bryce Harper could only throw the ball back to second base as Kozma scored the tying run.

“If I’m going to pitch where I want to pitch in the playoffs, that’s what you learn from tonight,” Storen said. “You got to take the emotions out if. We got a win, and I’m happy as hell about that.”

Storen struck out Matt Carpenter to at least push the game into extra innings. Given the state of the Nationals’ offense, the prospect offered little hope. They had scored two runs here Friday night, and Saturday they tossed up eight zeroes following Morse’s first-inning grand slam.

Adam LaRoche drew a leadoff walk off left-hander Sam Freeman to start the 10th. Roger Bernadina bunted him to second base, nearly sneaking the ball past Freeman’s athletic dive. With two outs and LaRoche still on second, Cardinals Manager Mike Matheny had Fernando Salas intentionally walk Danny Espinosa to pitch to Suzuki.

“You want to be in those situations,” Suzuki said. “I was excited they walked Espi. That kind of lights a fire under you.”

Espinosa provides more of a power threat, and as a switch-hitter he could face the right-handed Salas from the left side. But few Nationals have had better at-bats lately than Suzuki, slugging better than .500 in September. Against Salas, Suzuki roped a 2-2, 93-mph fastball off the fence. Both runners scored, and the Nationals’ dugout erupted.

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The relief sprung the rocky final innings. Jordan Zimmermann had allowed four hits, all singles, before two singles preceded Kozma’s one-out, two-run double into the left field corner in the seventh. The blow sparked a three-run inning, after which the Braves went final, letting the Nationals know they needed to win to chop away at their magic number.

“That [scoreboard] is big,” Manager Davey Johnson said. “Even with my old eyes, I can see it.”

A full, yellow moon hung behind the right field seats, and the Gateway Arch loomed behind center. The Nationals knew when they took the field they had a chance to clinch. “The finish line is in sight,” Jayson Werth said late Saturday afternoon.

The Nationals wasted no time trying to get there. With one out in the first, the Nationals pounced on Cardinals starter Kyle Lohse. Harper singled to center, the first of his three hits, making him 6 for his past 6 first-inning at-bats with two homers. Zimmerman doubled into the left field corner, and Lohse pitched around LaRoche to load the bases.

Morse smashed a low-and-away, 92-mph sinker deep to right field. The ball smacked off a facade behind the fence, pinballed off a ledge and came bouncing back on the field. First base umpire Chris Guccione signaled a fair ball, no home run.

Harper trotted home easily, but Zimmerman, having seen the ball clear the fence, did not realize a play was happening behind him. LaRoche became stuck halfway between second and third, and Morse was marooned between first and second. Second baseman Skip Schumaker caught the relay throw and raced Morse back to first base.

The play momentarily stood as a single with an out and only one run scored. Nationals players and coaches pointed to the outfield and implored umpires to review the replay. They obliged, quickly recognized their mistake and came out of the video room twirling their fingers.

The runners remaining on base started trotting home around the bases, until one of the umps halted Zimmerman. They explained that, to ensure all the runners touched each base, they had to return to their original bases before running home. Places, everyone!

Harper hopped out of the dugout. Morse had already rounded second, and he ran the bases in reverse until reached home.

“I guess I didn’t have to do that,” Morse said. “If I didn’t do it and they were like, ‘No, you’re out,’ I would never sleep again.”

His teammates hollered at him from the dugout to swing. He was not going to, he said, but Cardinals catcher Yadier Molina encouraged him to take a hack. So Morse stood in the batter’s box and acted every kid’s dream. He swung at air with a fake bat. You could almost hear Morse’s 9-year-old self thinking out loud: Here’s the pitch . . . the swing . . . grand slam!

“It was pretty cool,” Morse said. “It was pretty weird. I thought they were waiting for me to swing, and then everybody started running. It was such a crazy moment. Might as well have some fun with it.”

The four Nationals jogged around the bases and converged at home plate for high fives and hugs. Morse’s loopy grand slam had given the Nationals an instant 4-0 lead and created a new Washington baseball memory.

More memories and the playoffs are approaching. The Nationals have not yet clinched the East, but they have been battle-tested, and they have a chance tomorrow to do it without any help. They can take the title with one win, all by themselves.

“I like it,” Johnson said, a smile spreading on his face. “I’ll sleep good tonight.”