Ramiro Pena launches the two-run home run off Craig Stammen in the 10th inning that put the Braves ahead to stay after rallying to knot the game at 4-4 in the ninth. (Jonathan Newton/The Washington Post)

Ryan Zimmerman retreated to the video room late Friday night and replayed the central piece of the Washington Nationals’ unraveling. He saw himself throw what could have been the game-ending out into right field. Zimmerman watched Drew Storen stare into the outfield and chew on his mouth guard. He saw Davey Johnson gaze blankly from the dugout. It was all there — a defensive error, another stunned reliever and a manager trying to figure out how to halt the transformation of two of the Nationals’ presumed strengths into outright weaknesses.

In a 6-4, 10-inning loss at Nationals Park, the Nationals’ bullpen crumbled and their defense let them down. Tyler Clippard and Storen could not hold the three-run lead starter Ross Detwiler handed them after seven innings. The game-tying runs dashed home after Zimmerman fielded a chopper with the bases loaded and rifled the ball past Danny Espinosa at second base.

The disastrous ninth inning led to the ruinous 10th, when Ramiro Pena crushed a two-run home run over the home bullpen off Craig Stammen. As Stammen walked off the mound and fans fled for the exits, the collective ERA of Washington’s relievers stood at 6.34, second-highest in the major leagues.

“We need to do better,” Clippard said. “Ross pitched a hell of a game. It hurts. It hurts, obviously, for the club to get the loss. But it hurts for him. A bullpen, collectively, to have your starter do what he did and not get the win for him is very, very disappointing for us as a group and I know for me, too.”

The Nationals expected a tense confrontation in their first of 19 meetings with the Braves, who have lost only once this season, and their improved lineup. The divisional test, for one night, exposed a defense Johnson called “sloppy” even before the game and a bullpen trying to re-establish itself.

The Post Sports Live crew discuss the first two series for the Washington Nationals. After easily sweeping the Miami Marlins at home, the Nationals struggled against the Cincinnati Reds. (Post Sports Live)

Fair or not, the Nationals’ collapse in Game 5 of the National League Division Series last year will hover in the late innings all season. Friday night, Storen had his first chance to close since October, and the game slipped through the Nationals’ fingers.

“I don’t think panic is the right word,” Zimmerman said. “We definitely need to learn from our mistakes. It’s the same thing that kind of got us last year, and why we didn’t maybe move on, because we couldn’t close games out both pitching and defense-wise. We need to get better at that and learn from our mistakes.

“But this bullpen is really good, and they’ve been good for a long time. Just like as hitters, the league adjusts to pitchers. They’re going to have to look, just like we do, go back and see what the hitters are doing to them now. And now it’s their turn to adjust, just like we have to do.”

Johnson wondered about his own effect on the bullpen. Nationals relievers have thrown 32 2 / 3 innings, tied for sixth-most in the majors, despite a starting rotation with an ERA a hair over 3.00. Friday night, he rested closer Rafael Soriano because he had closed the previous three nights.

“We’re just not locating the ball. We’re all over the place,” Johnson said. “I’ve got to take responsibility. Probably overusing them or something. . . . Det’s pitched two great ballgames and come out with nothing. I feel real bad about that.”

The night could have been a celebration of Detwiler, who allowed just four hits and one run over seven impressive innings. The Nationals led, 4-0, after six, half their runs coming in the first when Bryce Harper smashed an opposite-field, two-run homer, his fifth of the season, off Braves right-hander Julio Teheran.

“I felt strong at the end,” said Detwiler, who has allowed one run in 13 innings. “Like I said, I wish there was less three-ball counts so I could have gone deeper. The bullpen has been taxed the last few days. They’ve been working pretty hard and I was kinda shooting to give them a night off.”

Instead, he handed them a 4-1 lead after seven. Clippard did not last one inning. He walked in a run in a 35-pitch, three-walk horror show of an eighth inning.

“My stuff’s good,” Clippard said. “I’ve been feeling really good as far as that’s concerned. Just the execution wasn’t there. My changeup was nonexistent tonight. I wasn’t able to put that where I want to, and that hasn’t happened in a long time. That was frustrating.”

Storen bailed out his former roommate — barely — when Dan Uggla’s 385-foot flyball settled into Denard Span’s glove on the edge of the center field warning track, leaving the bases loaded.

Storen escaped the eighth. He was not as fortunate in the ninth.

Chris Johnson greeted him with a line-drive single to center. Pena dropped a perfectly placed, surprise bunt single toward third base. A sacrifice bunt moved both runners into scoring position with one out. Storen struck out Andrelton Simmons, but Jason Heyward drew a walk, filling the bases for Justin Upton.

Upton chopped a grounder down the third base line, a seemingly harmless play, a potential game-ender. Zimmerman backed up to backhand the ball and, in an instant, surveyed his options.

He could have thrown all the way across the diamond, fired to second to nab Heyward or held the ball and give Storen another chance for the third out.

“Obviously, first base is out of the question,” Zimmerman said. “I’m not gonna beat the guy to third. I thought if I turn and make a perfect throw, I had a chance to get the guy bang-bang at second. Obviously, Heyward’s fast. It’s really tough as a competitor to just catch the ball and throw it back to Drew and just have the bases loaded. In hindsight, obviously that would have been the better play.”

Zimmerman turned and fired to second. Espinosa was still scurrying from where he began the play, stationed on the outfield grass. Espinosa arrived at the base at the same time Zimmerman’s throw skipped past him into right field. Even if Zimmerman’s throw had been on the money, it appeared Heyward would have been safe. Both Johnson and Pena scored, tying the game at 4.

“It’s easy to go back and look at that now, obviously,” Zimmerman said. “In the moment, I thought I should give it a shot. It didn’t work out too well. . . . It wasn’t a terrible throw. It just needed to be perfect.”

The late-game execution was far from perfect. Clippard, Storen and Stammen combined to walk five of the 19 batters they faced.

“That’s one of the things about being a bullpen that makes us special down there is that we have short memories and we understand that it’s a long season,” Storen said. “We’re going to swallow that, learn from it, and move on.”

The Nationals have little choice. They would report back to Nationals Park less than 12 hours after leaving, ready to face the Braves again, hoping Stephen Strasburg could outduel Tim Hudson. After 10 games, they have no need to panic. They do need to learn from what has gone wrong, even in the midst of a 7-3 start.

“Let’s get back out there,” Johnson said.