Bryce Harper hit his second career grand slam and seventh home run this season on Tuesday night against the Marlins. (Steve Mitchell/Usa Today Sports)

How does spontaneous combustion occur? How does a lineup, frozen in place, suddenly ignite like the Washington Nationals’ did in the seventh inning of Tuesday night’s 7-0 win over the Miami Marlins? How does six innings of near complete futility become a seven-run lead just like that?

“You don’t know why, you don’t know if it’s third time around, guys seeing somebody,” Manager Dusty Baker said. “. . . You don’t ask why or how come, you just accept it.”

Whatever the spark, the four home run inning it yielded was the first of its kind in Nationals history. Not even in the days of the Expos has this franchise hit back-to-back home runs twice in an inning. No team in all of baseball has done that since 2010.

That outburst — which included Jayson Werth’s 200th career homer, a towering shot from Wilson Ramos that threatened the Marlins Park roof, Bryce Harper’s second grand slam in a week, and Ryan Zimmerman’s first home run of the season — came after six hapless innings against Marlins starter Adam Conley. The young left-hander went scoreless inning for scoreless inning, strikeout for strikeout, with Stephen Strasburg.

The Nationals entered the game hitting .212 overall, .143 with runners in scoring position, in their last two games. They jumped at Conley early, so much so that he struck out eight Nationals and allowed four hits in six innings.

“The young man [Conley], he was pitching over there,” Baker said. “. . . He was throwing well, I mean big time.”

So was Strasburg. Nationals pitching coach Mike Maddux would call Strasburg’s most recently honed pitch a “cutter,” if he had to call it anything. Other players, even Major League Baseball’s pitch tracker, have identified it as a slider, and they are not wrong. No combination of slider and cutter yields a worthwhile nickname (“slutter,” for example, probably should not stick), so settle for cutter for now. Tuesday night, Strasburg used it against righties and lefties alike as part of an effective and efficient mix.

Strasburg threw the cutter to catcher J.T. Realmuto, who grounded it into a 6-4-3 double play in the second. He threw it to formidable left-handed hitters Dee Gordon (last year’s National League batting champ) and Christian Yelich (who entered the game leading the majors in on-base percentage), among others. With that pitch in his arsenal, he struck out 10 batters and allowed three hits over eight sparkling innings.

Still, the game headed to the seventh hopelessly scoreless. Daniel Murphy lined out. Up came Werth.

Werth entered the day hitting well below .200, his struggles well-documented, feeling what he called “a leak” in his swing that was making him inconsistent. As he fouled a few pitches off, he felt the trouble and tried to make an adjustment mid at-bat — “not the easiest thing to do,” he said. He laid off a change-up to get to 3-2 and thought a fastball was coming. It did come, and he hit it out to left-center for the 200th home run of his career, and in so doing lit the pilot light for what would become a historic inning.

“First one on the board, you think you’re going to win that ballgame the way Stras is throwing,” Harper said. “. . . I think everybody just doesn’t relax, but a calm goes over the dugout to play, have some fun and have some good at-bats.”

Next came Ramos, who entered Tuesday hitting .350 but had yet to showcase his power with consistency. Conley threw him a first-pitch fastball. Ramos hit a towering home run to left-center. 2-0.

“Most of the time, when somebody hit a home run, the next pitch is fastball,” Ramos said. “The other two at-bats, I was looking for the same pitch, I just missed it.”

Danny Espinosa hit a flyball to right next. Two outs. Then Strasburg singled for the second time — “just wanted to join in,” he joked later. Michael A. Taylor doubled behind him to put runners on second and third. Anthony Rendon walked.

Up came Harper. In came Marlins left-hander Chris Narveson.

Harper struck out twice Tuesday and said he was wondering what was going on to cause such trouble before realizing his stance was narrower than usual. He spread it out during that final at-bat, looked for a 2-1 cutter and got it. Strasburg scored from third, as he has on both of Harper’s grand slams.

“It’s probably all on me,” Strasburg joked.

Werth, more serious in his analysis, pointed out the way the lineup is balanced around Harper so that he can come up in bases loaded situations that force relievers to pitch to him. Then Werth called Harper “arguably one of the, if not the, best players in the game.”

“I wouldn’t have given him that kind of credit early on in his career,” Werth said.

Harper’s homer was his fifth in sixth games and seventh of the season. He hit his seventh home run of his MVP season on May 6.

Next came Zimmerman, who said he had been reaching for balls for a few at-bats now but finally “let one travel” into his zone. He hit it out to right-center, where it probably would have been a double last season before the Marlins moved the fences in, where it gave the Nationals a 7-0 lead.

How does spontaneous combustion occur? With little adjustments and a little luck, with a balanced lineup like this one, and with an ever-improving MVP. What does spontaneous combustion yield? A two-game losing streak snapped and a 10-3 record, second best in baseball.