A lonely fan takes in the Nationals-Marlins game in the upper deck on Tuesday night. (Marc Serota/Getty Images)

For all the lofty expectations surrounding these Washington Nationals, the third week of the season has arrived with the growing presence of uncomfortable trends. In an 8-2 loss here to the lowly Miami Marlins on Tuesday night, each element of potential worry reared its head.

Third baseman Ryan Zimmerman committed his fourth throwing error, leading to four unearned runs. Starter Dan Haren, the $13 million offseason acquisition brought in to shore up the back of the rotation, unraveled following the error, failing to complete the fifth inning. And a depleted lineup offered little resistance to a Marlins team that won for just the third time in 14 games.

“It’s still really early in the season,” Zimmerman said. “It’s April 16 and there’s a ton of games left. I really hope nobody is panicking or worrying.”

The Nationals were playing without outfielders Bryce Harper and Denard Span, two keys to the top of their lineup. Each was laid low by flu-like symptoms. Second baseman Danny Espinosa hasn’t played since Sunday after being hit by a pitch on the right wrist. In their places were Roger Bernadina in center field, Tyler Moore in left and Steve Lombardozzi at second.

Haren, 32, was seeking his second straight strong start when he took the mound on a humid night at Marlins Park. He churned through the first three innings, locating his fastball on both sides of the plate, adeptly mixing in a sharp splitter.

The Post Sports Live crew discusses whether the Nationals bullpen woes, Ryan Zimmerman’s throwing errors and Wilson Ramos’s injury are reasons to worry. (Post Sports Live)

He induced Juan Pierre to pop out to start the fourth before his evening fell apart. Haren got 37-year-old Placido Polanco to send a ground ball to Zimmerman, who ranged to his left to make the play. Zimmerman flung the ball to first and Adam LaRoche lunged forward to catch it, swiping at Polanco from behind his back. Polanco was safe, the throw ruled an error.

Zimmerman looked on disappointedly from across the diamond. October surgery was supposed to fix his troublesome throwing mechanics of last season, but this recent string of miscues has raised questions again. Just 14 games into the season, Zimmerman’s four errors have led to seven unearned runs. After Tuesday’s error, he even turned to teammates in the dugout for their thoughts.

“That’s why it’s so tough, too,” Zimmerman said. “Everything feels good. I long toss, my arm feels strong, everything’s good. It’s just a matter of me sticking with it and not mentally getting frustrated, just going out there and knowing that I can do that kind of stuff. I know I can do that.”

Zimmerman made two crucial errors last week but has been steadfast in his confidence in the shoulder, repeating Tuesday that it feels great. In the eighth inning, he made a slick barehanded play and threw across his body for the second out.

Manager Davey Johnson has stood by Zimmerman, acknowledging the third baseman likely wouldn’t feel completely comfortable with his shoulder and its strength until June.

Shortstop Ian Desmond stood in defense of Zimmerman, saying his throwing miscues are “not going to derail his stardom.”

“I would imagine his confidence is a little down if he’s coming to me,” Desmond said. “I have some things that I see, but I think he’s to the point now where it’s right there. He’s gotten 100 times better. Everything is already moving in the right direction. He makes one [bad throw] and then he makes five good throws. He’s moving in the right direction. And obviously having surgery doesn’t help anything, having to take time off and rehab and try to find that slot again.”

After Zimmerman’s throwing error, Greg Dobbs followed with a single, sending Polanco to third. Justin Ruggiano smacked a run-scoring single, then Haren hung a splitter to rookie Adeiny Hechavarria, who drilled it into the left field seats for a three-run shot, just the third home run for the Marlins this season. Haren used 34 pitches to complete the inning, 26 after the error. He needed 93 pitches to get through 41 / 3 innings, and his ERA sits at 8.10.

“Up to that [error], I was rolling, but I’ve got to be able to pick the guy up,” Haren said. “That’s part of baseball. They pick me up, I pick them up. I’m sure that he probably feels bad about the home run that the guys came around and score, but I mean, I’ve got to be able to pick him up. They taxed me pretty good that inning and I just didn’t have nothing after that.”

Throughout his 11-year career, Haren has averaged just over one home run per nine innings. This season, he has allowed five in 131 / 3 innings. He loaded the bases with three singles in the fifth inning and then walked Dobbs to give the Marlins a 5-0 lead. It was Haren’s first walk of the season. Johnson emerged from the dugout to lift him. For the second time in three starts Haren didn’t make it through the fifth. Even last season, Haren’s worst of his career thanks to back issues, only four times in 30 starts did he fail to make it through the fifth inning.

“I feel like the ball’s coming out all right,” he said. “I’ve learned to pitch with a little less velocity. In 2011 I had a great year and I wasn’t throwing any harder than I’m throwing now in the American League. Probably need to go back and look at that stuff, pitch more like that. Whatever I was doing then. But yeah, I’m searching right now. I’m searching for answers. I’m trying in between starts and I’ve got to get better. I do. I feel worse about it than anybody.”

The Nationals offense squandered opportunities against Marlins starter Alex Sanabia, who allowed six base runners in the first three innings. His sinker helped him strand them all. Moore and Lombardozzi doubled in the sixth to account for both Nationals runs. Of the Nationals’ six losses, three have been blowouts by six runs or more.