Denard Span loses the ball in the fog at Wrigley Field. (David Banks/Getty Images)

The conditions at Wrigley Field on Thursday were eerie and ominous. Instead of a hot Chicago day in late June, thick fog hovered over the city all day. The apartment buildings and rooftop seats just outside the stadium were out of sight all afternoon. Every half-inning, thick fog rolled in and out, making it hard for players to see. Outfielders were fuzzy masses from the stands. It looked and felt like fall.

Against the Chicago Cubs, one of the worst teams in baseball, the Washington Nationals also produced a bizarre result. The normally efficient Doug Fister wasn’t, and he allowed three runs. Steady reliever Craig Stammen couldn’t keep the game tied late, giving up a decisive double just after the Nationals pulled even. The Nationals’ base running was off, and the offense came to life late but didn’t do enough in a 5-3 loss. The fog created by a cooler-than-normal Lake Michigan only made the day more unsettling.

“It was different,” Stammen said. Added center fielder Denard Span: “Just unusual here in the Midwest.”

Fister entered Thursday’s game in a groove, posting a 2.03 ERA in his previous eight starts. He pitched through the fog and the Cubs’ lineup, one of the least productive in baseball, for three innings. In the fourth, Fister put the Nationals in a hole.

Fister allowed a single to Justin Ruggiano on a low fastball, a pitch that normally produces a groundball. Then Fister battled the Cubs’ best power hitter, Anthony Rizzo, for eight pitches, leaving the last one up and leading to a double to put runners on second and third. Fister then went right at cleanup hitter Starlin Castro. Fister fired a fastball inside and off the plate. Castro broke his bat flaring the pitch to left field, and two Cubs scored.

After the Nationals split a series against Atlanta, the Post Sports Live crew debates whether they have reached a turning point against the Braves. (Post Sports Live/The Washington Post)

“I felt like I was executing, but at the same time the pitches need to be a little better,” Fister said. “The pitches need to be a little better. I need to make sure they’re in or out a little bit more. If I get it in a little bit farther on that jam shot over the infield, who knows. A lot of shoulda, woulda, couldas.”

In the next at-bat, Fister unfurled a wild pitch that put Castro in scoring position, a mistake that would prove costly with one out. Welington Castillo singled in another run to give the Cubs a 3-0 lead.

Throughout the night, the fog threatened both teams. Span made a handful of difficult plays through the haze. With two outs in the sixth, Fister got Luis Valbuena to sky a ball to center field. Span, however, couldn’t see the ball in the thick fog, throwing up his hands. The ball fell in, left fielder Ryan Zimmerman raced to find it, and Valbuena settled for a triple.

Fister escaped that inning with a lineout, but the fog was so bad that umpiring crew chief Jerry Layne told Nationals shortstop Ian Desmond that he was considering a potential delay, according to Nationals Manager Matt Williams.

“But it’s not like rain where you’ve got radar and you can see, ‘Okay we’ll delay it 15 minutes and it’ll be gone,’ ” Williams said. “You just have no idea. But both teams had to play with it.”

“We’re in the Midwest, man,” Span added. “I played in Minnesota for five years, and it’s unpredictable. Never remember it being like this, but all year round, it’s unpredictable.”

Against Cubs starter Travis Wood, the Nationals were unpredictable, too. They have been one of the best teams in the majors when facing left-handed pitching (a .280 team average), and Wood entered Thursday’s game with a 4.55 ERA. But Wood blanked the Nationals for five innings.

In the first inning, Wilson Ramos singled to left and the Nationals tested left fielder Ryan Sweeney. Zimmerman, who reached on a double, was waved home by third base coach Bobby Henley. Sweeney hit the cutoff man, third baseman Valbuena, who easily gunned down Zimmerman at home.

The Nationals made up for their squandered opportunities with a productive seventh inning. After missing 14 games with a hamstring strain, Ramos led off the inning with a walk. Danny Espinosa followed with another walk.

Fister was up next, and Williams sent him to the plate to lay down a sacrifice bunt, which Fister did. In that situation, Williams could have used a pinch hitter such as Scott Hairston, who hits left-handers well, as Fister wasn’t going to take the mound in the bottom of the inning, anyway. But Williams saw a tiring pitcher in Wood and knew Span doubled in his previous at-bat, so he liked that matchup.

“Figure we’d get those two guys in scoring position and tie it with one swing as opposed to trying to go after it with more than one,” Williams said.

Span, the next batter, drove in both runners with a line-drive double off the ivy-covered wall in right field that knotted the score at 3. But Span overran second base and was thrown out, erasing the chance for Anthony Rendon to bat with a runner in scoring position. The Nationals drew five walks and smacked seven hits but scored only three runs because of wasted opportunities with three double plays, strikeouts and base running slip-ups.

“You’ve just got to keep grinding,” Williams said. “The fact that we came back and tied it is good. It just wasn’t our night.”

Only moments after the Nationals tied the score, Stammen took the mound in the seventh and couldn’t protect it. With one out, he gave up a double to light-hitting Darwin Barney and then walked Chris Coghlan. He fell behind Ruggiano with two outs and then left a 2-1 fastball over the plate. Ruggiano, who entered 5 for 8 lifetime against Stammen, smacked a two-run double to left to give the Cubs a 5-3 lead. The ball landed perhaps less than a foot fair.

“Got to shut them down after we get the momentum and keep the momentum somehow,” Stammen said. “And I made a couple pitches that got the momentum in their favor, and they capitalized.”

The Nationals brought the tying run to the plate in the eighth inning, but Zimmerman grounded into an inning-ending double play. The Nationals went down in order in the ninth, ending a strange day.