Jordan Zimmermann reacts after giving up a three-run home run to Dioner Navarro during the fifth inning. (Charles Rex Arbogast/Associated Press)

Washington Nationals General Manager Mike Rizzo sat in the visitors’ dugout at Wrigley Field on a pleasant Monday afternoon and explained both his hope and despair. Earlier in the day, he pulled off a surprising trade for veteran outfielder David DeJesus, a pricey bench player he felt could help address one of his team’s weaknesses. With less than six weeks left in the regular season, he still believed the Nationals’ playoff hopes weren’t over.

But to make an improbable postseason run, Rizzo believed the team’s underperforming offense needed to deliver — “do the little things” — and its starters had to continue pitching well. Both were completely absent Monday night in the opener of a four-game series at Wrigley, an 11-1 drubbing by the rebuilding Chicago Cubs that ranks among the Nationals’ worst losses in a season full of bad ones. Jordan Zimmermann yielded three home runs and eight runs, and two relievers allowed another two long balls. Wilson Ramos’s homer was the Nationals’ lone extra-base hit.

Fantasies of playoff runs have no room for clunkers like this.

Even before Rizzo watched the Nationals endure their 64th loss, which matched their 2012 total and put them 101 / 2 games behind the Cincinnati Reds for the National League’s second wild-card spot, he described his frustration. The lack of success despite the talent has been mind-boggling.

“It’s frustrating to the players that are involved, it’s frustrating to the coaching staff and to me,” he said. “It’s hard to put your finger on, but I do see an extremely talented bunch of guys that are grinding it out every day, and the amount of effort and caring that they’ve put into this team is honorable for them.”

No matter how hard they tried, the Nationals couldn’t overcome Zimmermann’s struggles. One of baseball’s best pitchers in the first half of the season, Zimmermann has stumbled in recent weeks, and it continued on Monday. He left balls up in the strike zone and was hammered. His three home runs allowed tied a career high. Normally an innings-eater, he lasted only five. He left the game with the Nationals trailing 8-0, having matched a career high in runs allowed.

Through the first three months of the season, the right-hander posted a 2.28 ERA in 16 starts. Since the beginning of July, he has posted a 5.96 ERA. Zimmermann believes he rushed his delivery, but wasn’t sure that was the problem. His stuff has been good, but not his command.

“I’m not hitting my spots right now,” he said. “The fastball’s up. I’ve got to do a better job of locating.”

Cubs right fielder Nate Schierholtz, a left-handed hitter who hammers right-handed pitching, launched a three-run homer to right off Zimmermann in the first inning. The Nationals had little hope after that. Zimmermann admits he can stomach allowing solo home runs, but homers after allowing a double and a walk, then hanging a curveball, are tougher.

“He feels pretty good,” Manager Davey Johnson said. “It’s frustrating when you feel good and you’re getting hit. It’s all about making pitches, making pitches to set up pitches. Especially in this ballpark. . . . He’s a tremendous pitcher. He’s going to be fine.”

Schierholtz launched another home run in the seventh inning off left-handed reliever Fernando Abad. Third baseman Donnie Murphy smacked two homers of his own, one off Zimmermann and the other off Ian Krol. Catcher Dioner Navarro clobbered a three-run homer off Zimmermann in the fifth, after the right-hander again allowed a double and walked a batter. If the Nationals were already frustrated with their disappointing season, their performance on Monday was depressing.

Johnson began subbing out his regular players by the sixth inning, beginning with third baseman Ryan Zimmerman. DeJesus made his Nationals debut against his former team, receiving a standing ovation when stepped into the batter’s box against Cubs starter Jeff Samardzija in the eighth.

The Nationals could muster little against Samardzija, who allowed only six base runners in a complete game. Ramos was the lone National to solve Samardzija, hitting a pitch out of Wrigley Field and onto Waveland Avenue just beyond left field. A fan threw the home run ball back over the stands and the crowd cheered.

Monday was the 33rd time this season the Nationals have scored one run or fewer. The Cubs, on the other hand, had scored only 12 runs in their previous six games.

Samardzija “just pitched a heck of a ballgame,” Johnson said.

After the game, Rizzo walked through the cramped Nationals clubhouse as players ate and changed in silence. Minutes before, Johnson reiterated his belief in the team’s talent but again acknowledged inconsistencies. Ramos stood at his locker and explained his own motivation.

“It’s a hard game,” he said. “Hard to come back. But we never can put the head down. We have to keep fighting all nine innings and see what happens. You never know.”