Second baseman Anthony Rendon stabs a line drive off the bat of Miami’s Adeiny Hechavarria in the third inning, offering a scant highlight from Washington’s lackluster loss. (Alan Diaz/Associated Press)

In the midst of the worst inning of the worst start of his career, an expressionless Stephen Strasburg stood on the mound and listened. He had walked three of the first four batters he faced, and first baseman Adam LaRoche came to talk. After a bases-clearing triple, pitching coach Steve McCatty emerged from the dugout. Following the inning’s third hit, shortstop Ian Desmond paid a visit. When the opposing pitcher singled, catcher Wilson Ramos tried.

The misery continued. In the 63rd start of his career, Strasburg experienced a new low, yielding a career-high seven earned runs on five hits and four walks over two laborious innings in an 8-3 loss to the Miami Marlins. He trudged off the mound after 66 pitches and six outs as the Washington Nationals lost for the fourth time in five games. The defeat didn’t damage the Nationals’ standing in the National League East as they’re still six games behind the Atlanta Braves, but it dealt a blow to Strasburg’s pride.

“I couldn’t throw a strike,” he said. “It’s frustrating.”

What happened on the field Friday turned baseball logic on its head. In 10 previous starts against the Marlins, Strasburg had a 2.77 ERA. The Marlins, a young and rebuilding team on a historic pace for offensive ineptitude, were owners of the worst offense in the majors, hitting a collective .232 and averaging 3.27 runs per game.

Strasburg, meantime, appeared poised to build on an impressive first-half résumé. He came into Friday’s game with a 2.45 ERA, allowing opponents just a .209 batting average. He had allowed seven runs in his previous three starts combined. He had been bedeviled by a lack of support, the primary reason his record stood at just 5-6 and likely why he wasn’t originally included on the National League all-star team. But when the Nationals scored three times in the first, everything seemed in place for him to even his record.

The Post Sports Live crew debates whether Bryce Harper will have a more exciting appearance in the MLB All-Star Game or in the Home Run Derby. (Post Sports Live)

“Pretty shocked,” LaRoche said. “I don’t think anybody in the ballpark saw it going that way. We jump out on top, get a pretty good roll going and come back and give it away. That’s tough. That’s a lineup that typically doesn’t score a lot of runs going against one of the best pitchers in the game. To jump on him like that is pretty wild.”

Handed a 3-0 lead thanks to LaRoche’s two-run double and a run-scoring grounder by Jayson Werth, Strasburg’s control was off from the start. Home plate umpire Jerry Layne’s tight strike zone may have contributed somewhat to the problem, but many of Strasburg’s pitches weren’t close. Ramos could see Strasburg’s command was shaky in the bullpen before the game.

“For me, right now, he’s thinking too much,” Ramos said. “He just has to go out there and throw his pitches. To me, thinking too much. Right now, first inning, he walked one guy, he had his head down. I don’t like to see that. But we got time to talk, and hopefully next time will be better.”

With the bases loaded, Strasburg’s first pitch to Marcell Ozuna was far outside. The next pitch was a 94-mph fastball down the middle that Ozuna clobbered deep to center for a bases-clearing triple. Strasburg has fought his mechanics on the mound plenty of times before, but this time he couldn’t recover.

“That’s my thing: If I fall off to the first base side too much, then everything gets out of whack,” he said. “I’ve been battling through it the last couple starts, been able to make the adjustments, and [Friday] I just couldn’t do that.”

Strasburg fell behind 2-0 to Derek Dietrich, including one pitch that was borderline, and the third pitch, a low fastball, was smacked to right for a run-scoring single. Two more singles brought in another run. The inning, the worst Strasburg has ever produced, ended on his 36th pitch with a groundout by Justin Ruggiano, who led off the inning with a walk.

Manager Davey Johnson sent Strasburg to the mound in the second, and he again labored. Behind 1-2, Ed Lucas worked a seven-pitch walk. Facing slugger Giancarlo Stanton, who has a long history of killing the Nationals, Strasburg jumped ahead 0-2 with two called strikes. Stanton, however, stayed alive and then demolished the seventh pitch of the at-bat over the right-field wall for a two-run shot.

The Post Sports Live crew discusses Bryce Harper’s “play me or trade me” text to Davey Johnson and whether the outfielder has too much control over when he plays. (Post Sports Live)

“It can happen to anybody, but it’s kind of remarkable to happen to him,” Johnson said of Strasburg’s night.

Strasburg finished the second, then disappeared into the dugout and clubhouse. Ross Ohlendorf pitched four strong innings in relief, allowing only one hit and two walks. Since joining the bullpen nearly three weeks ago, Ohlendorf has been solid as a middle reliever, lowering his ERA to 1.74 with Friday’s performance.

After their fast start, however, the Nationals produced nothing. In the seventh, a rally was snuffed out by the cavernous dimensions of Marlins Park. With Denard Span and Desmond on base, Bryce Harper crushed a ball off left-hander Mike Dunn to deep center field. Ozuna ran it down at the warning track, about 410 feet from home plate. Harper, frustrated, slammed his helmet into the dirt around first base.

An inning later, Werth crushed a ball with two outs high into the air, nearing the light fixtures, but that landed in front of the left-field wall and was misplayed by Ruggiano. Anthony Rendon walked, but Ramos grounded out softly to end the threat.

The Nationals, however, lost the game in the first inning. Even with the seven earned runs, Strasburg carries a 2.99 ERA. He may still be selected as an injury replacement for teammate Jordan Zimmermann for the Midsummer Classic in New York. But if not, Strasburg will have to wait at least a week away before he can return to the mound and flush his career-worst start from his system.

“You’re always trying to get better, always trying to learn,” he said. “And I think it’s these type of games where you’ve got nothing working that you can just kind of take a step back and just pick it apart a little bit, see your flaws a little bit more.”