Visited again by expectation and the promise of meaningful baseball, the Washington Nationals this weekend produced an unvarnished mess. For three weeks, the Nationals generated hope for a thrilling September. Saturday night against the New York Mets, their first hit came on an infield single off a relief pitcher’s bat when they trailed by eight runs.

The Nationals have made a small margin of error for themselves if they want to sneak into the postseason, and losing a series to the Mets at home does not fit the parameters. After the 11-3 shellacking they absorbed at Nationals Park, they can only avoid a sweep Sunday. Dan Haren couldn’t make it out of the third inning, the Nationals’ previously scorching lineup flailed against right-hander Zack Wheeler and mistakes dotted their performance.

“That one put me back in the hospital,” Manager Davey Johnson said.

The final month of the season will begin with the Nationals trailing the Cincinnati Reds by 7 1 / 2 games for the National League’s second wild-card spot. The Nationals had won 14 of 19 games before the Mets, another piece of a favorable schedule, arrived at Nationals Park. The notion of the Nationals making a run at the second wild card and redeeming four disappointing months had become vividly real. It veered closer to fantasy with two losses to the 62-72 Mets, the first a nail-biter and the second a dumpster fire.

“We know that we’re running out of time,” center fielder Denard Span said. “Each game that goes by, it’s getting even more and more [instrumental] for us to win. Tonight, just a terrible game. The type of loss like this came at the wrong time.”

The Nationals walked Wheeler with the bases loaded to force in a run. Anthony Rendon sparked a three-run Mets rally in the eighth against Ryan Mattheus after he patted the ball in his glove and allowed Eric Young Jr. an infield hit. Bryce Harper, after a day of complaints about his effort, hustled into an out trying to stretch a double to a triple with no outs, down by nine runs.

“Little things like that and the dam breaks,” Johnson said.

Haren exited after he had recorded eight outs, and he would be charged with seven runs. Haren’s rotten night owed to misfortune as much as lifeless pitches with poor location. The first three Mets who put a ball in play made outs. Nine of the next 10 recorded hits. Only one of those was not a single, and the two-run double by Omar Quintanilla deflected off Span’s glove.

“It probably wasn’t going to be my day,” Haren said. “I felt great. Stuff was good. I told you guys honestly if I had good or bad stuff that day. My stuff was fine. It wasn’t that. Balls fell in.”

“A thousand little paper cuts,” Johnson said. “I don’t think they hit the ball that hard, but a lot of hits.”

In the second inning, with two on and two outs, Quintanilla ripped a line drive to center field. Span raced to his left and made a diving, backhand effort. The ball deflected off his glove, perhaps an inch separating Haren from the end of the inning. Instead, as Span barrel rolled, both runners churned home to give the Mets a 2-0 lead.

“I mistimed it,” said Span, who collected three hits to extend his career-best hitting streak to 14 games. “I definitely wish I could have caught that for Dan. I think if I would have caught that, it would have changed the game.”

In the third, Haren recorded two outs. One out scored a run, and the other out came only after a base hit. He could have avoided disaster had a one-hopper back at him, a possible double play, gone past him rather than hitting his glove. Ike Davis smacked a sacrifice fly to left field to make it 4-0. Two batters later, Jayson Werth threw out Josh Satin with a perfect, one-hop throw from left field. When Matt den Dekker flicked an RBI single to left — the first hit of his career — Johnson trudged to the mound.

After Tanner Roark jogged from the bullpen, the third inning only grew uglier. Roark walked Quintanilla to load the bases for Wheeler. He threw the opposing pitcher three consecutive balls, and after he came back with two strikes, he walked in a run. Young poked a single to left to score one more run.

“Everything that could go wrong in that second or third inning did,” Johnson said.

The Mets led 8-0, and the only question left to answer was how Harper would respond to the mini-controversy caused by his jogging to first base Friday night. He answered in the eighth, when he led off with a screaming liner into the right field corner.

As he raced around second base, Harper’s helmet flew off his head. Right fielder Juan Lagares rifled a throw to second baseman Daniel Murphy. He fired a one-hop throw into third base. Harper dove head first, dirt flying in his face, but the perfect relay beat him by inches. As Harper dusted himself off and walked off the field, the crowd showered him with a standing ovation.

Johnson had a different reaction. He felt Harper had allowed the chatter about his hustle to affect him and make an unwise baseball decision.

“He needs to quit listening to all this stuff,” Johnson said. “He’s a good baseball player. He’s got great baseball instincts, but sometimes he gets overwhelmed with all the stuff going on. He’s still young in that regard. Gets caught up in playing the game. Still learning.”

In the ninth inning, fans roared as the wave traveled around the stadium. The Nationals knew their pursuit of a playoff spot could not be perfect, that they could not win every game left on their schedule, no matter how easy. But the losses did not have to double as nightmares.

“It’s one of my worst nightmares, dropping a series to the Mets,” Johnson said. “But we just need to turn it around, starting tomorrow. Just almost sweep out. That’s what we’ve got to do.”