Bryce Harper strolls into third base with his fourth triple of the season in the sixth inning, but he later struck out with the bases loaded and one out in the eighth inning to all but seal the Nationals’ fate in Miami. (Lynne Sladky/Associated Press)

Bryce Harper carries with him a plan each time he walks into a batter’s box. He thinks deeply about the situation, what the pitcher will do and how he should react. Tuesday night in the eighth inning, with the bases loaded and the Washington Nationals trailing by a run, Marlins Park erupted around Harper and the game fell into his hands. Harper distilled a simple conclusion. “I went up there,” he said, “to hack.”

Harper, then, would harbor no regrets about the next three pitches, even if his strikeout would provide the pivotal moment in the Nationals’ 3-1 loss to the Miami Marlins. Harper chased a fastball at his eyes from side-winding right-hander Steve Cishek to suck the air out of the rally. Ryan Zimmerman ended it with a groundball to third base. Their last, best chance had been quashed, and their fourth series loss of the season awaited.

The Nationals had taken the lead with a suicide squeeze, executed by a batter who prayed he had read the sign correctly, and against a pitcher, Anibal Sanchez, they cannot beat. They lost it after one debatable decision and one wayward pickoff throw, one of Edwin Jackson’s lone missteps over 62 / 3 strong innings. Harper missed an inside-the-park home run after a faulty read. But their most crucial moment came in the eighth, when the Nationals loaded the bases, sent their best hitters to the plate and walked away with nothing.

“We had them in a spot where we should at least score a run,” Manager Davey Johnson said. “We had the right guys up. It just didn’t happen. Frustrating.”

A taut, well-pitched game entered the eighth with the Marlins leading, 2-1. Xavier Nady sparked a rally with a pinch-hit, leadoff single. Johnson and Marlins Manager Ozzie Guillen exchanged personnel. Cishek, a right-hander who throws 93 mph from his belt, walked Danny Espinosa and Steve Lombardozzi to load the bases with one out.

Up walked Harper. One run would tie the score, and all he needed to do was send the ball to the outfield. He didn’t care that Cishek had thrown eight balls in nine pitches. When Cishek started him with a fastball down the middle, he hacked. Foul. Cishek threw another sinker on the inside half, another foul.

“They were pitches I could handle,” Harper said.

Cishek had him down 0-2, and he flung another fastball, over the plate and about six feet off the ground. Harper flailed and missed. He walked back to the dugout. Afterward, when asked about being overanxious, Harper nearly cut off the question.

“Absolutely not,” he said calmly. “I was trying to get something to the outfield to score that runner. When I look back on that at-bat, I felt great. There’s nothing I can do about. I don’t feel over-anxious at all. I’m going up there to hit something.”

Said shortstop Ian Desmond: “You’re talking about a guy that’s throwing sidearm, 92 miles an hour. That’s not your average pitcher. I’m not mad that he swung at it. I’d rather him swing than take one right down the middle.”

Zimmerman’s groundout ended the rally for good. The Nationals fell behind by two runs in the bottom of the inning when Hanley Ramirez crushed a homer off Craig Stammen. In his first major league at-bat in the ninth, Jhonatan Solano gave the Nationals hope with a two-out double.

Sanchez held the Nationals without a hit for the first four innings, hardly a surprising turn of events. Sanchez entered the game 7-0 in his career against Washington with a 2.10 ERA.

Desmond led off the fifth with a single, and he turned it into a rally by stealing second and taking third on catcher John Buck’s high throw. Desmond remained on third after Rick Ankiel struck out.

Both managers prepared for a low-scoring game. Guillen pulled his infielders on to the grass, a concession to Jackson’s early dominance. Against Sanchez, the Nationals had inspired little confidence in Johnson. “We were pounding the ball,” Johnson said afterward, sarcasm dripping from his voice.

In the batter’s box, after running the count to 1-1, Corey Brown looked to third base coach Bo Porter and was pretty sure he saw him right — was that a suicide squeeze? On Monday and Tuesday, Porter had reviewed the Nationals’ signs with Brown, freshly called up from Class AAA Syracuse.

“I didn’t do too well passing the test,” Brown said. “I was kind of hoping that I saw it right.”

He had. Brown swallowed and squared to bunt — he had never, at any level of baseball, attempted a squeeze. Desmond charged home as Sanchez delivered. Brown deadened a change-up. Desmond glided over the plate as Buck scooped and fired to first. The Nationals’ dugout greeted Desmond and Brown like conquering heroes, and they led 1-0.

After another scoreless inning for Jackson, Harper gave the Nationals a chance to add to their lead. With two outs in the sixth, Harper demolished a first-pitch change-up to the right-center field fence, some 400 feet away from the plate, a mammoth flyball that would have been a home run in many parks.

Harper hurtled out of the batter’s box with his typical ferocity. Marlins center fielder Bryan Petersen leaped at the fence and crumpled to the ground. Harper slowed to a stop around second base, believing Petersen had robbed him. But the ball was on the warning track, next to Petersen.

“I got to second base and I thought he caught it,” Harper said. “I was like, ‘Ah, crap.’ It should have been an inside-the-parker, actually. I should have kept going.”

Harper settled for a triple, his fourth in only 29 games, and Zimmerman grounded out to strand him.

Harper’s pause became key after the next inning. In the sixth, Omar Infante ripped a one-out double, just the second hit Jackson allowed, and he moved to third base with two outs. Up stepped Giancarlo Stanton, who looms over the field like a kid too old for Little League.

Stanton has been perhaps the most frightening hitter in the majors this month. If you would ever considering putting the go-ahead runner on base, even in a big ballpark, this would be the time. Johnson left the decision up to Jackson. With left-hander Logan Morrison up next, Jackson wanted Stanton.

“You just have to pick your times when you want to come after them and the times when you don’t,” Jackson said. “You’re going to have situations where you’re going to have to come at ’em and you just take your chances. Here it is. Best stuff against best stuff. Sometimes you win it, sometimes you lose it.”

Stanton won. He lashed a 1-1, 92-mph fastball to the corner in left field, a double that tied the score at 1.

The Marlins took the lead in the next inning. Chris Coghlan singled with one out, and Jackson turned it into an instant rally. He tried to pick off Coghlan, and his wayward throw bounded to the fence.

“I just snatched it a little bit,” Jackson said.

Coghlan scooted to third. Pinch hitter Greg Dobbs flied to left field. Brown settled under the ball and made a strong, accurate, one-hop throw, but Coghlan simply beat it. Coghlan flashed the “safe” sign, the park erupted, and the Marlins had the lead.

The Nationals gave themselves an ideal chance to take it back. Harper went down with the game on the line, but he went down hacking.