Home plate umpire CB Bucknor tosses Braves Manager Fredi Gonzalez for arguing balls and strikes in the fifth inning following a walk to Jayson Werth. (Jonathan Newton/The Washington Post)

The magnitude of the Washington Nationals’ task struck as the innings wore on and the life drained out of Nationals Park. For a month the Nationals had kept slim postseason hopes alive the only way they could — by winning almost every day. The euphoria of all those wins obscured the difficulty they faced. They sprinted across a tightrope for five weeks, and Wednesday night they slipped.

Can they recover? Every loss and every day peeled off the calendar hurts the Nationals so much more than any win can help. And so their 5-2 loss to the Atlanta Braves — just their second defeat in 12 games — left their season on the canvas, the referee’s count nearing 10. Even a series win felt hollow.

“It’s just not enough,” Manager Davey Johnson said. “We just can’t afford to lose. It’s that simple.”

The Nationals seized a two-run lead as Ross Ohlendorf rolled through five scoreless innings. But the Braves’ menacing bullpen held them scoreless after Ohlendorf made three mistakes in the sixth and gave back the lead on Justin Upton’s two-out, two-run homer. Craig Kimbrel, the untouchable closer the Nationals had brought down Tuesday afternoon, returned to his flawless form in the ninth.

“I feel like that’s probably about as good as I’ve pitched,” Ohlendorf said. “I’m just really disappointed in the way it came out.”

The Post Sports Live crew tries to see meaning in the Nationals’ late season run even though the team is a long shot to make the playoffs. (Post Sports Live/The Washington Post)

As they walked back to their clubhouse Wednesday night, the Nationals confronted the dreary prospect of relying on the 100-loss Houston Astros, who went into extra innings with Cincinnati. Eventually, the Reds won, 6-5, in 13 innings to drop Washington to 51 / 2 games back in the race for the second National League wild card.

Throughout the Nationals’ surge, Johnson has espoused the same goal. Ninety wins, he says, and he likes their chances. To reach that figure, the Nationals would have to win nine of 10.

“It gets harder,” first baseman Adam LaRoche said in the Nationals’ clubhouse, a few feet from a TV. “That’s why we got the Reds game on now. It’s tough counting on another team to melt down for you.”

The Nationals get to face the last-place Miami Marlins four times this weekend in their final home series of the year, but they won’t have expected starter Stephen Strasburg on the mound until Saturday. Johnson pushed Strasburg back from his Thursday start after the pitcher felt a sensation “like a strong cramp” Wednesday in his ailing right forearm before he warmed up. Gio Gonzalez will pitch in his place.

The Reds have to play the Pittsburgh Pirates six more games. Still, the Nationals’ outlook requires optimism.

Ohlendorf retired the Braves’ first 10 batters and, despite Upton’s one-out single in the fourth, faced the minimum through five innings. Alex Wood matched Ohlendorf zero for zero until the fifth, an inning he would exit like a drunken college kid thrown out of a bar and yelling at the bouncer.

The Nationals loaded the bases against Wood with one out for Jayson Werth, perhaps the league’s best hitter since the all-star break. When the count ran 3-2, Wood tried to sneak a 92-mph fastball inside, a coin-flip ball-strike call.

Werth raised his arms. Catcher Brian McCann framed it on the corner. Home plate umpire CB Bucknor lifted his arm and pointed to first: ball four. Wood screamed expletives at Bucknor from the mound until Manager Fredi Gonzalez scurried to home plate, at which point Bucknor ejected Gonzalez.

“People told me inside it was outside” the strike zone on replay, Johnson said. “It doesn’t merit that kind of reaction at any time.”

Once the uproar subsided, Bryce Harper rocked a sacrifice fly to center, sending the Nationals ahead 2-0. The Braves pulled Wood. As he walked off the mound, Wood pointed at Bucknor and cursed at him. Bucknor ejected a pitcher who had already been taken out.

In recent starts, Ohlendorf had cruised through five innings and then lagged. But Ohlendorf needed only 57 pitches for his first 15 outs Wednesday night. He had his best slider in months and felt strong on a cool night. Johnson sent him to the mound with the bullpen behind him dormant.

The first pitch Ohlendorf threw in the sixth was an 89-mph fastball, one of the slowest he had thrown all night. Dan Uggla hammered it about 15 rows beyond the left field fence.

Jordan Schafer followed with a bunt that rolled between the mound and first base. Ohlendorf scampered to his left, scooped the ball and launched it over LaRoche’s head. Schafer motored to third with no outs. Ohlendorf energized the crowd with a strikeout and a pop-up.

As two relievers warmed in the bullpen, pitching coach Steve McCatty trudged to the mound. “Be careful with him,” McCatty told Ohlendorf as Upton walked to the plate.

Once McCatty left, Ohlendorf threw a first-pitch slider, trying to locate it down and away. It floated chest high over the plate. Upton smashed it into the red seats. The haymaker left the Nationals reeling and, suddenly, trailing 3-2.

“I felt really good at the end,” Ohlendorf said. “I just made a couple bad pitches.”

The Braves would tack on two more runs, and the Nationals’ hopes would grow dimmer. They had made the improbable seem so real for so long, and then it just felt plain improbable.