WASHINGTON — When the energy faded inside Nationals Park, then faded again, and then faded some more, it was replaced, in its entirety, by the feeling that comes when the World Series slips out of a firm grasp.

Washington wasn’t used to that before Saturday night. Now it will be. Because the Nationals fell to the Houston Astros, 8-1, once their starter faltered and the offense couldn’t pick him up. That evened the series at 2-2, back to square one, with the Astros ready to throw their aces the rest of the way. Patrick Corbin gave up four earned runs in six innings of grinding work. The Nationals’ bats were cold for a second consecutive contest, managing just four hits, moving each of Corbin’s mistakes beneath a microscope.

A Game 3 loss on Friday was defined by missed opportunities for the Nationals’ offense. This Game 4 loss was marked by generating few opportunities at all. Washington loaded the bases with one out in the sixth and could only score a run. Juan Soto plated it by chopping out to first. Howie Kendrick followed with an inning-ending strikeout. And in the next half, with everything slipping, Alex Bregman crushed a grand slam off Fernando Rodney. Cheers boomed out of three sections dotting the stadium. They were all filled with Astros fans. The rest of the crowd was quiet, stewing, stacking patience against their sinking guts.

And their silence was loud.

This weekend began with a line of kids walking through the Navy Yard, just a block from the stadium, chanting “Go! . . . Nats! . . . Go!” on a cool morning. Nationals banners hung from porches and in storefronts. Nationals talk — lathered in optimism, lacking the restraint of past falls — blared through car radios and restaurant TVs. The city’s hosting its first World Series since 1933. That was evident. Then 43,876 people came to see what lies beyond imagination.

But then the Astros took two days to dent the Nationals’ runaway faith. Washington had won eight straight, going back to the Oct. 7, before Houston had its away against Aníbal Sánchez and the offense flatlined in Game 3. The Nationals went 0-for-10 with runners in scoring position. They were sloppy in the field, making two errors, and it all gave Houston a second life. Saturday became a pivotal turning point.

The on-paper strategy once favored the Nationals, at least before a pitch was thrown. Corbin is a front-line lefty who signed for $140 million last winter. The Astros turned to José Urquidy to kick off a bullpen game. They lack a definitive fourth starter. So after Gerrit Cole, Justin Verlander and Zack Greinke go, they lean on a mash-up of relievers to give their bats a chance. It was always the one contest Washington would be favored in. They just had to turn logic into results.

Yet Urquidy was dominant, throwing five scoreless innings, while Corbin couldn’t hold the Astros down. Corbin was tagged for two runs in the top of the first, on four straight hits, and his pitch count spiked up to 26. The Astros turned two get-me-over sinkers into singles. He couldn’t locate his slider, his best pitch, and slipped again when Robinson Chirinos lifted a two-run shot off him in the fourth.

It was Chirinos who bounced into a double play to help Corbin escape the first. Before that at-bat, with Corbin struggling, pitching coach Paul Menhart walked to the mound for a short conference. Corbin followed by throwing two change-ups to Chrinos, a pitch he typically uses just 5 percent of the time, and soon retired him with an inside sinker. So, in their second matchup, Corbin attacked Chirinos with his ninth change-up of the outing. It fluttered into the middle of the zone, like a one-winged bird, looking ready to be swatted. Then it flew high over the stadium and landed deep in the left-field seats.

Chrinos slapped his chest while skipping toward home plate. Corbin stood by the mound, some 60 feet away, his shoulders slumped and his face blank. He is known for handling big moments with a personality that doesn’t even quiver. But that’s been absent for four of his seven playoff appearances. He is the first player in history to make three starts and four relief appearances in the same postseason. If his arm is tiring, and the workload is too big, he’d likely never say. It just lengthens the list of problems Washington has to solve. And fast.

Rotation depth was supposed to separate the Nationals in this series. The offense charged back-to-back wins to begin the series in Houston. But Corbin wilted, the offense did, too, and the Astros widened the gap when Tanner Rainey and Fernando Rodney shrank in the seventh inning. Manager Dave Martinez turned to Rainey, then Rodney, to hold a three-run deficit in place.

He had Sean Doolittle and Daniel Hudson sitting in the bullpen after two full days of rest. The decision backfired when Rainey couldn’t find the strike zone, Rodney couldn’t avoid hard contact, and, after Bregman’s blast and five walks in the inning, the deficit ballooned.

The Nationals have scored just twice through 18 innings in their own ballpark. They are 1-for-19 with runners in scoring position across those two games. The lone hit did not even score a run. They are picking the worst time to dig up old habits — a lifeless bullpen, poor situational hitting, caving in October — and will now face Cole, Verlander and, maybe, Greinke with their title shot back in the balance.

Their saving grace is that Max Scherzer and Stephen Strasburg will be on the mound for the next two games. The only way to swallow Saturday was to remember, somehow, that the Astros did all this to catch up.