Nationals center fielder Roger Bernadina (2) looks into the outfield after getting the last out of a loss to the Cubs. Washington was seeking a four-game sweep and, with a win, would have been guaranteed to be above .500 at the all-star break. (Toni L. Sandys/WASHINGTON POST)

After an overdue offensive outburst, an epic unraveling and an instant comeback, the Washington Nationals ultimately absorbed the kind of stomach punch they had become so expert at delivering. The Nationals spent the early portions of Thursday night making the act of winning look, for once, like something other than a small miracle. Then they made the act of losing feel like abject disaster.

The Nationals led the Chicago Cubs by eight runs in the fourth inning, an advantage they had never failed to convert into a victory since baseball returned to Washington. They then completed the largest blown lead in franchise history, rallied to tie the game and then lost, 10-9, before 22,016 at Nationals Park after a Cubs rookie flared a 98-mph fastball into the right field corner in the ninth inning.

Darwin Barney’s double off Henry Rodriguez provided the final salvo in a torturous loss for the Nationals, who had moved to the precipice of a rare high-water mark. Had they turned their lead after the fourth into a four-game sweep of the Cubs, they would have moved to three games over .500 for the first time since May 2010. It would have ensured, at worst, a .500 record entering the all-star break.

Instead, they capped a string of improbable victories with a loss more improbable than anything that preceded it. Afterward, Manager Davey Johnson blamed himself for keeping starter Livan Hernandez in the game one batter too long. The Nationals entered the sixth inning up 8-0. After five consecutive two-out hits, culminating with Blake DeWitt’s three-run missile of a homer off the foul pole, the Cubs had turned an eight-run laugher into a two-run nail-biter.

“That was a tough one,” Johnson said. “I’m going to have a tough time sleeping tonight on that one.”

The Nationals’ clubhouse fell silent, but only out of protocol and decorum, not depression. Players insisted this loss, even with its crushing nature, would be no different from any other. They had won this series, and they would try to win the series that starts Friday against the Colorado Rockies.

“I think you’ve got to look at the big picture here,” right fielder Jayson Werth said. “We’ve been playing some really good baseball. A loss is a loss, however you want to throw it up there. I don’t think this loss is that big a deal. We can get over this one, no problem.”

Their pitching staff has carried the Nationals all season, but Thursday it only produced a list of culprits. After Hernandez started the meltdown, three relievers pitched, and all of them gave up an earned run. The biggest blow came when Carlos Pena smoked the first pitch Sean Burnett threw — a slider over the plate with one out in the seventh — into the first row in right for a two-run homer that tied the score at 8.

“I just need to pick up my slack,” said Burnett, whose ERA rose to 5.76 after his sixth blown save. “I’ve been pretty bad all year, making guys throw more pitches than they have to by coming in for me. I need to step up and start executing.”

After the third inning, it would have been hard to fathom a clubhouse competing over who deserved blame. Before Thursday night, the Nationals hadn’t scored more than five runs in a nine-inning game since June 21. Then the first eight men to the plate in the third reached base, culminating with the two-run hit to left by Wilson Ramos that knocked out Matt Garza and gave the Nationals a 6-0 lead. The Nationals added one more run on Roger Bernadina’s second hit of the inning, and by the time it finally ended the Nationals had sent 12 men to the plate in the and scored seven runs, their most in one inning this season.

The Nationals took their 8-0 lead after Rick Ankiel’s RBI double in the fourth. Hernandez carried the lead with ease into the sixth. Hernandez surrendered three straight singles with two outs, then a double to Barney that made it 8-3. In other circumstances, Johnson would have yanked Hernandez. But he wanted to rest a wornout bullpen, so he let Hernandez face DeWitt.

“That one, you chalk up to me,” Johnson said. “I was just trying to save some guys in the bullpen. They’ve been overworked. I gambled. That’s what I did. I gambled with my starter.”

DeWitt, pinch-hitting in the pitcher’s spot, cranked a 1-2, 86-mph sinker off the foul pole in right field. Later, Johnson called that the clear turning point.

“Ninety-nine percent of the time, we win the game when it’s 8-0,” Hernandez said. “It’s one bad inning that changed the whole game. It’s baseball. Sometimes, baseball is crazy like that.”

The Nationals trailed for the first time shortly after Rodriguez retired the first two batters he faced in the eighth. Starlin Castro doubled, and Aramis Ramirez ripped an RBI single off the tip of Danny Espinosa’s glove as he leaped high in the air. Silence overwhelmed the park, and a 9-8 deficit hung over the Nationals.

Michael Morse answered in the bottom of the inning with a two-out single up the middle to score Bernadina, who had singled – his third hit of the game – and stolen second.

In the bottom of the ninth inning, with two outs and the tying run on third base, Bernadina roped a line drive to right field. The crowd had seen this movie before, and they recognized a happy ending. A cheer went up, until it turned into a gasp as the ball fell into a glove.

In their past three games, all one-run victories, the Nationals had scored their winning run on a wild pitch, an infield single and a suicide squeeze bunt. The one-run victory wouldn’t come Thursday.

“We’ll come back tomorrow and play hard,” Hernandez said. “This is what we do. We’ve got to come back tomorrow and win. That’s the only way we can leave this game in the past.”