Sean Doolittle — part of the Nationals’ new-look bullpen — and catcher Matt Wieters celebrate the team’s 9-4 win Sunday. The victory clinched the season series for the Nationals, who could see the Cubs again in the NLDS. (Jonathan Daniel/Getty Images)

Who you gonna call?

Brandon Kintzler, Ryan Madson and Sean Doolittle, apparently.

When the Nationals’ bullpen door opened Sunday at Wrigley Field, the accustomed assortment of ghouls, goblins, zombies and floating gobs of ectoplasm that Washington baseball fans have come to regard as normal this season did not appear.

Instead, Oliver Perez, then the newly arrived trio of Kintzler, Madson and Doolittle — not actually dressed as Ghostbusters but serving much the same purpose — took the mound. They proved that if you throw a swift fastball to a precise part of the strike zone, and they threw 38 of their 45 pitches for strikes, it’s much like “crossing the streams.”

Bad, scary hitters — like Kris Bryant, Anthony Rizzo and Willson Contreras — disappear. Good things — like 11 soft, unfrightening final outs for the Cubs — befall you. With this brand-new bullpen competence as inspiration, the Nats, trailing 4-1 when their relievers arrived, erupted for eight runs in their final three at-bats to thud the Cubs, 9-4, win their weekend series two games to one, clinch the season series with Chicago four games to three and, probably, send a message, too.

What message is that? The psychomagnotheric slime that has infected the worst-on-earth Nats bullpen all season, slathering everybody with icky late-inning nightmares, appears to have been sent back to another dimension. As every fan of the “Ghostbusters” franchise (like Dr. Peter Venkman, a.k.a., Bill Murray, Cubs fan) would know, psychomagnotheric slime has the power to heighten a person’s mood either negatively or positively.

Maybe that’s what happened to the Nationals’ bullpen for months. Each failure brought depression and anxiety that contaminated the whole group’s mood. Then the psycho slime — some would call it the team mood and momentum of a baseball season — was free to do its worst.

That pinky-purply goop can also animate inanimate objects. Once, it made a toaster dance to Jackie Wilson. The mood of the wooden bats in opposition dugouts suddenly became buoyant, feeding on the euphoria, until no Nationals lead was ever safe. That’s how you throw away eight virtually locked-down leads, including six games when the Nats led going into the ninth inning.

That’s my theory, and I’m sticking to it. The slime has been busted. The same trio of Kintzler, Madson and Doolittle, acquired by General Manager Mike Rizzo in the days — and in Kintzler’s case, the last seconds — before the July 31 trade deadline, got the last eight outs of a 4-2 Nationals win Friday. The Nats now have a normal, uncursed bullpen, and maybe, as other arms get healthy, even quite a good one.

And why wouldn’t that be the case? The bullpen the Nats bought north for Opening Day had individuals with plausible credentials. But as a unit it was ineptly constructed. Not to beat a dead horse, but — hand me that two-by-four — the Nats had used 11 men in their bullpen this season before seeking desperate reinforcements. Ten of them had a career total of six saves. Is that a joke? The 11th, Shawn Kelley, had a big heart, two Tommy John surgeries and 11 saves.

The new trio have all been closers at various times and have 167 career saves in 1,099 games. Are they a major upgrade? Duh, yeah.

Perez has been effective all year and often dominates even good lefty hitters. He’s also a trivia answer: Who are the three Nats pitchers with more than 1,000 career innings who rank in the all-time top 10 in strikeouts per nine innings: Stephen Strasburg (second, 10.5), Max Scherzer (fifth, 10.2) and Perez (10th, 9.5).

If Matt Albers remains effective, off-the-disabled list Sammy Solis pitches as he did Saturday when he fanned four of five Cubs he faced, Koda Glover returns to health with his early season stuff-plus-attitude and Enny Romero’s 101-mph arm feels better, the Nats might develop quite a nasty mix-and-match October bullpen here even if it lacks a famous closer. Maybe not, too. But others, like Joe Blanton and Kelley, are allowed to be their best selves, too. Stay tuned.

This Wrigley weekend might have had significance beyond the first appearances in the seventh, eighth and ninth innings by Kintzler, whose late-moving fastball and slider allow him to challenge everybody; Madson, who’s throwing 96 to 99 mph (faster than he ever has in a fine career); and the spunky almost-all-fastballs-all-the-time Doolittle.

The Nats have been ignoring waves of injuries and usually playing their best against winning teams (18-11) all season, but their defiance in the face of a world champion Cubs team that was almost completely healthy for the first time all season was genuinely impressive. These clubs aren’t fond of each other. Trea Turner’s hand — broken by a Cubs fastball in late June, after Turner had run wild on Chicago for four days — hasn’t been forgotten. Yet the Nats entered this series without their Nos. 1-2-3 starters — Scherzer, Strasburg (DL), Gio Gonzalez (paternity leave) — or even their No. 5 starter in Joe Ross (DL for the year).

Yet they won this series behind Tanner Roark, emergency pickup Edwin Jackson and rookie Erick Fedde, who looked promising in his second career start, keeping his poise and aggression despite allowing three homers while fanning seven.

All season, the Nats have had to play above the distraction of a bullpen that has lost seven games with a lead of two or more runs in the eighth inning. That’s about five more than an “adequate ’pen.” The Nats should be about 70-39, not 65-44. Morale has stayed high, but with hints of fraying, with grumbling from many in the organization, top to bottom, who are usually stoic soldiers.

If Sunday is a hint, morale worries from bullpenitis may soon be a dead issue. Seldom does the feeling of a chunk of a season change more swiftly than it did for the Nats in the span of four pitches in the eighth inning.

Perez, who escaped a jam in the sixth, helped by a Matt Wieters pickoff of Jason Heyward at second base, and Kintzler, with a crisp seventh, had set a tone. After Bryce Harper beat out a dribbler with one out, the Nats, trailing 4-3, showed the Cubs their trademark strength this season — the instant mega explosion.

Ryan Zimmerman, still steamed at all the walks the Cubs had issued to Harper last year to get to him, hit a rocket double off the center field ivy, Daniel Murphy was intentionally walked and Anthony Rendon was hit in the arm by a slow 1-0 curveball to tie the score. Just like in pulp sports fiction, Wieters seized the moment when the Cubs were most likely to be deflated — a blown lead by their bullpen. He hit Carl Edwards Jr.’s first pitch over the center field bricks for a grand slam.

Two months from now, this past weekend — which many Nats followers, including me, watched on TV, expecting little, anticipating perhaps a series of Cub slugfests — might be superseded for symbolism by any of a dozen factors.

But right now it feels like the Nats’ injured players will start returning soon and the process of becoming nearly whole and sharp in time for the playoffs will begin. One thing, however, might be very different. By then, the Nats might have quite a deep bullpen and quite an above-average one, too. Watch out, slime.

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