What the Washington Nationals have done this season is like going into your backyard with a spade to plant petunias and, instead, striking oil.

Their appointment with the World Series, just 14 days after facing elimination in the wild-card game, is like spilling water on Grandma’s painting of an old farm house and finding out she had painted over a still-pristine Picasso.

The Nats’ pennant-winning, 7-4 victory over the St. Louis Cardinals in Game 4 of the National League Championship Series on Tuesday night began as a massive gleeful party, constructed on an amazing seven-run first inning that had a crowd of 43,976 attempting to prove that mass delirium is possible. For two hours, Nationals Park witnessed a romantic comedy: Town loves team, team loves town, and the Cardinals roll over and play dead to end this four-game sweep.

But by the late innings, this game — even with a huge NLCS lead — felt like a zombie slasher meets Frankenstein’s bigger brother as closer Daniel Hudson escaped a bases-loaded eighth-inning jam by getting Matt Carpenter, the go-ahead run, to ground out.

In the end, the bullpen of Tanner Rainey, Sean Doolittle and Hudson held the fort for the last dozen outs — a plot twist almost beyond comprehension for one of the worst bullpens in 50 years. But it was the fitting ending in a year when the Nats tweaked, fixed or worked around every problem.

That such a bullpen would now stand tall just fits the whole season-long theme: There is no gift like the unexpected gift, no joy like the jubilation when the next emotion you anticipated was sadness.

“Some of the best things come from the unexpected moments,” said postseason hero Howie Kendrick, who was named the NLCS MVP.

There is no shock like the discovery that a desperate moment — May 23 for these Nats — that felt like the end of an era of success was really a time of transformation under duress into something better, richer and more satisfying than you had imagined possible.

Just when it felt like the best era of Washington baseball since 1924 to 1933 was swirling down the drain, with the Nats’ record at 19-31, suddenly everything that seemed wrong began to go right.

The struggling and lame — Trea Turner, Anthony Rendon and Juan Soto — came back from the injured list and got hot. The team landed a Baby Shark named Gerardo Parra on a one-ounce test line — picked up free, with the San Francisco Giants still paying his salary. And the team that knows how to put the huge, ugly “E” in “elimination game” became the first team in major league history to win two of them in the same October after trailing by three or more runs.

The Nationals — once known as the “Natinals” on their own jerseys, the same team that got knocked out of the first round of the playoffs four times — celebrated the patriarch of D.C. baseball by claiming the pennant on Ted Lerner’s 94th birthday. His team knows what it has given him. And he understands what he has given to this city for the first time in 86 years.

“I want to tell the fans, ‘This is for you!’ ” Lerner said in the postgame celebration.

“We earned the 12 games under .500 [in May]. We were bad,” said General Manager Mike Rizzo, ripping off a list of all of his team’s early-season sins and injuries. “But we also earned the [.675 winning percentage] the rest of the way.”

The Nats go to the World Series as just what they love to be — disregarded, constantly underdogs. They will face an American League champion, the Houston Astros or New York Yankees, that will be regarded as much their superior. But the Nats are certain in their baseball guts that this will be darn close to a toss-up World Series.

“These guys back here, they cured my heart,” said Manager Dave Martinez, his face split with grins after being rushed from a game to the hospital just four weeks ago with what he feared was a heart attack.

Two points, both apparent in Game 4, should be made about these Nats — akin to noting that lightning cannot only electrocute you but also knock down trees on your head.

In their past 123 games, only the Yankees have scored more runs per game. The Nats’ lineup, in their current state of perfect health, is one of the deepest and most multifaceted in the majors.

Game 4’s seven-run first inning epitomized the Nats’ versatile attack — one that’s out of step with the home-run-or-whiff model of this era. Yes, the Nats hit homers — 231, but that was only 13th best this year. Within the NL, they were first in on-base percentage, tied for first in batting average and second in fewest strikeouts. They also tied for the league lead in steals. To many, all of this is heresy. But it has worked, with a master-class example in the first inning.

The Nats scored seven runs without hitting a ball farther than 275 feet in the air. They slapped a single (Turner) and double (Soto) to the opposite field. A power hitter (Rendon) put the first pitch he saw in play because he knew it could produce a sacrifice fly. Two players merely put the ball in play: Ryan Zimmerman sharply and Victor Robles with a popup. The Cardinals made an error on the first and completely missed the second as it fell among three of them. Yan Gomes and Turner followed with two-run singles drilled through the left side of the infield. Between them, pitcher Patrick Corbin put down a perfect sacrifice bunt.

It was, frankly, nothing less than baseball high art: The first 10 hitters of a game with the pennant on the line executed perfectly.

Dakota Hudson, the Cardinals’ wins leader, left having gotten one — o-n-e — out.

The other Nats weapon that has brought them to this city-delighting pennant is depth. In World Series games played in the AL city, the Nats will be able to pick a bat off their loaded bench to be the designated hitter — perhaps switch-hitting Asdrúbal Cabrera (91 RBI), or Brian Dozier or Matt Adams (20 homers each). There might even be a spot for Parra — who got a hit, to universal delight, in the pennant clincher.

In the glee that now sweeps over Washington, don’t bet the house on the Nats beating the 107-win Astros or 103-win Yankees. But it might be worth taking out a second mortgage on your gardening shed.

Whatever ills or joys are still to come, Tuesday night was the best baseball victory in D.C. since 1933, another era when America seemed chest-deep in serious problems. In October 2019, Washington is united behind one flag and one purpose — symbolized by those silly Baby Shark bandannas.

The Nats are also a team for their place and time. They exalt in their diversity with eight key players, and team leaders, from Venezuela, Brazil and the Dominican Republic. Martinez told his Latin teammates when he arrived in the minors in 1983, “Sorry, but I don’t speak Spanish.”

Now, of course, he does. But he has also learned a lot about another language that he struggled with when he took the job last year: He is closer to fluent in “bullpen.” He has learned at least four words — Doolittle, Hudson, Rainey and Rodney. And he used that vocabulary well in Game 4, getting a scoreless inning from Rainey in the sixth. Doolittle blanked the Cardinals in the seventh, and Daniel Hudson completed a scary eighth before a perfect ninth to end it.

All of these factors are part of the explanation of why the Nats’ NL championship is neither magic nor fluke. It is excellent, but some of it hides in plain sight.

This, however, is also a team with a fire deep inside it that it seldom fully articulates. This is a band of old men without rings.

Only one National, reliever Hunter Strickland, has played for a World Series winner. After Game 2, Zimmerman and Max Scherzer, both 35, referred to themselves, and the 16 other Nats on this playoff roster who are past their 30th birthdays, as “Los Viejos” — the Old Men.

“Everybody wants to forget the old guys,” said a jubilant, hat-backwards Scherzer amid the infield celebration. “Well, we went out and won the National League pennant!”

For Washington, it has seemed as if it took a baseball eternity to win a pennant. But to three-quarters of these Nationals, winning the NLCS may mean more than just the D.C. joyride of a visit to the World Series.

To them, grabbing a pennant, marvelous as that is for their city and its fans, is probably — though none will say it — a steppingstone to their collective dream of rings.

If you think Game 4 was hard as that 7-0 lead dwindled to 7-4, and that those comebacks in elimination games against the Milwaukee Brewers and Los Angeles Dodgers were harrowing, be forewarned. What these old men, plus a few gifted youngsters, with their dugout dancing and hugging, really have in mind, starting next Tuesday, will be even more challenging. Perhaps even impossible.

But, as we have learned, the prize that is least expected, the goal that seems almost impossible, is also the most thrilling.

Pop the corks. Raise the pennant. But know one thing: The Nationals don’t think their season has reached its peak.

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