Bryce Harper, left, and Ryan Zimmerman, right, both scored in the Nationals’ four-run first inning. (Kevin C. Cox/GETTY IMAGES)

The opener of the Washington Nationals’ biggest series yet this year — perhaps their biggest series in seven years — reached a crucial point Friday night in the seventh inning. Their four-run lead over the Atlanta Braves had withered to one. The fifth spot in their starting rotation had become an open competition. Two runners stood in scoring position. There were two outs.

Ryan Zimmerman stood in the on-deck circle, and he recognized immediately what was happening. Tim Hudson, long his nemesis, threw four obvious balls to Bryce Harper, openly bypassing the Nationals’ 19-year-old prodigy to face the face of their franchise with the bases loaded. Zimmerman shrugged.

“Bryce is better than me right now,” Zimmerman said. “I’d walk him, too.”

Zimmerman delivered the key hit, a bases-clearing double that let the Nationals cruise to a 7-4 victory at Turner Field that stretched their division lead over second-place Atlanta to two games. The Nationals’ four-run first inning gave them enough cushion to survive Ross Detwiler’s laborious 41 / 3 innings before Chien-Ming Wang restored order and added drama to the Nationals’ pitching picture.

In the end, Zimmerman’s second double off Hudson — a right-hander whom he previously had one extra-base hit against in 48 career plate appearances — provided the difference to one of the Nationals’ biggest wins in years.

“That’s why they have me in the lineup where I am,” Zimmerman said. “I’m supposed to get hits like that.”

After Detwiler allowed three runs on five hits and four walks, Wang made the sixth relief appearance of his career and fired three strong innings to earn the win — and to state his case that he deserves Detwiler’s spot in the rotation. Detwiler has allowed 16 earned runs in his past 201 / 3 innings over four starts, and Manager Davey Johnson indicated he would consider switching him and Wang.

“Yes and no,” Johnson said. “I don’t make any decisions right after a ballgame. Emotions are running pretty high.”

Wang retired eight of the 11 batters he faced, his biggest mistake coming on a home run by Jason Heyward. Sean Burnett and Tyler Clippard recorded the final five outs to give the Nationals the early edge in the series.

The victory gave the Nationals more than a typical upper hand in the series. After the Nationals beat their nemesis in the first game of the series, they get to send Stephen Strasburg and Gio Gonzalez — their top two starters and two of the best this year in the majors — to the mound to try for the sweep.

“I like the way we’re set up,” Johnson said.

Wang allowed two inherited runners to score but fired three strong innings to earn the win — and to make a bid for Detwiler’s spot in the rotation.

Through an interpreter, Wang said he had not heard anything other than he will stay in the bullpen. But he impressed his teammates, frequently hitting 94 mph with his sinker. He said he feels stronger now than during spring training, when Nationals officials considered him one of their top three starters.

“He looked absolutely awesome,” shortstop Ian Desmond said. “I thought they were going to let him keep on going, to be honest.”

Hudson entered Friday night at 14-3 with a 2.05 ERA against the Nationals in his career, and he had never endured an inning like the first. Harper sparked the rally with a line-drive single to center field. Zimmerman entered the game hitting .174 against Hudson, then blasted Hudson’s second pitch about 400 feet to right-center field, a double off the fence.

With two outs, Desmond delivered a clutch two-out, two-run chopper up the middle that looked like a frozen rope in the box score. Rick Ankiel finished off the rally with a two-run triple, and the Nats led 4-0.

Detwiler walked to the mound with a four-run lead before he had thrown a pitch. He never found comfort. Detwiler walked two of the first seven batters he faced. He took 72 pitches to get through his first three innings. He craned his neck and stared into the sky after hits, snapped his glove at the ball when the catcher tossed it back to him and yelled obscenities after walks. His shirt soaked through with sweat.

“I kept trying to make little adjustments, and nothing was changing in the end result,” Detwiler said.

Atlanta struck for its first run in the third, but Detwiler plodded into the fifth holding a 4-1 lead. Despite awful command, his stuff — a fastball that reached 95 mph and a sharp breaking ball — allowed him to strike out five Braves in the first three innings.

Michael Bourn led off the fifth with a double, and Dan Uggla reached on a one-out walk on Detwiler’s 100th pitch. Johnson had seen enough, and he hobbled to the mound on a big toe that had been operated on Thursday.

“I was a little disappointed in Det that he didn’t take charge and go right after them,” Johnson said. “He kind of messed around with them. I like to give them every opportunity to get five, but I was just getting a little frustrated with the fact that he wouldn’t go right after them.”

Wang jogged in from the bullpen. The Nationals had stashed him there because they had nothing else they could do with him, really, as long as Detwiler — one of only two left-handed starters — stayed in the rotation.

“I was just trying to do my job,” Wang said.

Wang threw a first-pitch sinker to Matt Diaz, who smoked a double to right-center field. The Nationals threw out Diaz trying to stretch the hit into a triple with a well-executed double cut, but the Braves had slashed the lead to 4-3.

Hudson, meanwhile, recaptured his typical form against the Nationals after the four-run first. He faced one batter over the minimum for 52 / 3 innings, until Wang came to bat with two outs in the seventh. Wang may be one of the most helpless hitters to ever put on a major league uniform, but Hudson walked him on five pitches. Steve Lombardozzi doubled to bring up Harper with men on second and third.

The Braves showed Harper, who had a single and a hard lineout, uncommon deference with Zimmerman due up next. Zimmerman couldn’t disagree.

“It’s no disrespect to them or me or anyone,” Zimmerman said. “That’s just the game. Hudson against me or Hudson against a left-hander. I’m pretty sure he’s better against righties, and I know he’s better against me. That’s just the smart play.”

Zimmerman, incredulous at the call, took strike one over the inside corner. He whiffed at the next pitch to make it 0-2.

“You got to throw the plan out the window,” Zimmerman said. “Just battle or hope he makes a mistake.”

Hudson did. Hudson’s cutter stayed at Zimmerman’s thighs, and he belted it to the gap in left-center. The bases cleared. The Braves had made a calculated risk. And the Nationals, in first place even with an uncertain fifth spot in the rotation, are now the kind of team that sometimes gives opponents two bad choices.