Nationals starter Livan Hernandez left the game with a 6-3 lead after six solid if unspectacular innings, but the Nationals’ bullpen surrendered the lead — and the game — in the seventh and eighth innings. (Morry Gash/AP)

Henry Rodriguez spent most every moment of this season as an afterthought on the Washington Nationals’ roster until Tuesday night, in the eighth inning, when the bullpen gates swung open and, of all pitchers, he walked out. Manager Jim Riggleman handed him the ball, a one-run lead and a season that has started teetering.

Taking the mound with the bases empty and one out, Rodriguez allowed the Milwaukee Brewers to seal a furious comeback by scoring two runs and stealing a 7-6 victory from the Nationals at Miller Park.

The Nationals finally received signs of life from their sputtering offense, including three hits — one of them a grand slam — from first baseman Michael Morse. But they squandered a four-run lead as they lost for the sixth time in seven games, perhaps their most nightmarish defeat in their worst string of games this season.

The Nationals had been 11-0 this season when scoring six runs or more. But nothing is going right for them now, a fact made solemnly clear when Morse — who walked to the plate in the ninth inning 9 for 17 in his career at Miller Park — flied to right field to end the game after the Nationals had loaded the bases with two outs against closer John Axford.

“It’s gut-wrenching, man,” reliever Tyler Clippard said. “It’s rough. We’re in a rough stretch right now. We got to stay positive. These losses hurt, especially a game like this. We’ve got to win this game.”

The Nationals knocked out starter Chris Narveson after scoring six runs off him in 31 / 3 innings. But they managed one hit and no runs against three Brewers relievers in 42 / 3 innings, an offensive lapse that gave the Brewers the chance to come back.

And so they did. In the seventh inning, Rickie Weeks blasted a two-run homer to left field off reliever Clippard, a cutter left too high in the zone that suddenly shrunk the Nationals’ lead to 6-5.

Sean Burnett started the eighth inning by forcing a weak grounder to third from Prince Fielder, the only batter Riggleman wanted Burnett to face. Usual closer Drew Storen had thrown 25 pitches Monday night in an 11-3 loss because he needed work, so he could not pitch more than one inning.

Cole Kimball and Todd Coffey were options, but Rodriguez had allowed no runs on two hits and no walks in his past five innings. Riggleman decided the time had come to bring Rodriguez, acquired when they sent Josh Willingham to Oakland, into a taut game. “Rodriguez has been outstanding as of late,” Riggleman said. “To tell you the truth, I thought it was pretty obvious.”

So in came Rodriguez, who had pitched with a lead only once, with the Nationals up seven runs against the Baltimore Orioles.

“I felt normal,” Rodriguez said through interpreter Javier Castro. “That’s the game situation where I want to be. You just got to focus on the job and do your job.”

Casey McGehee was the first batter Rodriguez faced, and he shot a single to right. Rodriguez followed by striking out Mark Kotsay with a 100-mph fastball. Two outs, a runner on first. Harmless. But then Rodriguez showcased his other side, walking pinch-hitter Brandon Boggs on four pitches, moving the game-tying run to second. Danger.

Up came Jonathan Lucroy. Rodriguez started him with two strikes, and after Lucroy fouled off a pitch, he blooped a ball down the right field line — “a jam shot,” Rodriguez said.

Cruelly for the Nationals, the ball hit the chalk. McGehee scored easily. Boggs, improbably, wheeled around third and bolted for home on the single. Jayson Werth fired to first baseman Morse, who skipped a throw home. Just before Boggs barreled into him, catcher Wilson Ramos dropped the ball, and Boggs scored the winning run.

“When the runner is coming into the catcher and the ball is coming there at the same time, you’re trying to get a sense where the runner is and everything,” Riggleman said. “He was out if we were able to hold the ball.”

But Ramos dropped it, the final layer to a brutal loss. The Nationals had finally given Livan Hernandez some run support, some of which he generated himself with an RBI single. In his three previous starts, the Nationals had been shut out every game. In the start before that, they scored one run for him. In his first 10 starts, the Nationals had been shut out four times and scored 20 total runs.

Morse, having become the everyday first baseman with Adam LaRoche on the disabled list, ensured that dubious stretch of poor support would end. He blasted a grand slam in the third that put the Nationals ahead 6-2. Morse is 16 for 39 (.410) with three home runs and three doubles in May.

Tuesday, it was not enough. After their latest loss, the Nationals may be wondering what is.

“Sometimes, things happen in baseball,” Hernandez said. “We couldn’t do nothing.”