Matt Wieters grimaces after lining into a game-ending double play to seal a 3-1 loss to the Braves in the nightcap of a doubleheader Tuesday at Nationals Park. (Patrick McDermott/Getty Images)

Before the Washington Nationals handed the ball to Max Scherzer, the bona fide ace they pay to pitch big games, in Tuesday’s nightcap against the Atlanta Braves, they gave it to someone they never envisioned shouldering substantial responsibility this season. Jefry Rodriguez, the 25-year-old with an ERA pushing 7.00 in his brief major league career, was their choice for Game 1 of Tuesday’s pivotal doubleheader at Nationals Park. Thin starting pitching depth left them without viable alternatives.

The objective was to survive with Rodriguez and the bullpen before having their workhorse run with Game 2 to finish off a vital sweep against one of the two teams they’re chasing in the National League East.

But the Nationals didn’t sweep the Braves, and it wasn’t because Rodriguez failed. Washington trounced the Braves, 8-3, in the opener behind the best start of Rodriguez’s short career before wasting another strong outing from Scherzer in a 3-1 loss. The split kept the Nationals (58-55) 4½ games behind the second-place Braves (61-49) in the NL East and six games behind first-place Philadelphia, which beat Arizona, 5-2, late Tuesday night.

It was a squandered opportunity to gain two games in the playoff race, one they may regret in a couple months and could cost them another key bullpen piece for some time.

Kelvin Herrera, Washington’s closer with Sean Doolittle on the disabled list, exited the second game in the ninth inning with an apparent injury after surrendering the go-ahead two-run triple to Ender Inciarte. The triple, placed just inside the right field line, bounced off the wall in foul territory. Bryce Harper misplayed the carom and leisurely retrieved it as the second run scored.

Moments later, Herrera, who allowed hits to three of the four batters he faced, was walking off the field with trainer Paul Lessard. After the game, Manager Dave Martinez announced Herrera left with shoulder tightness. He’s scheduled to undergo an MRI exam Wednesday morning.

“His ball was coming out okay, but when I saw him [shake his arm] I thought there was something wrong,” Martinez said. “So [catcher Matt] Wieters went out, then we went out and I asked him what was wrong. He said his shoulder was tight. I said, ‘That’s it, you’re done.’ ”

Scherzer had held his own, limiting the Braves to one run on four hits over seven innings. His only blemish was yielding a home run to Charlie Culberson in the sixth inning.

He walked one batter and struck out six, including Dansby Swanson with a 97-mph fastball on his 113th and final pitch. At the plate, he went 1 for 2 to extend his hitting streak to six games and raise his batting average to .300.

But the only run support he received came in the first inning, when Juan Soto clobbered an 0-2 fastball from left-hander Sean Newcomb for his 14th homer in 68 games. The home run came after Soto went 2 for 2 with three walks in the opener to become the first teenager to reach base five times in a game since Robin Yount in 1975.

The Braves were poised to erase their deficit in the fourth inning. Freddie Freeman led off with a walk. Nick Markakis then singled to advance Freeman to third base. Scherzer was in a jam. But he wiggled free, retiring Kurt Suzuki, Inciarte and Johan Camargo in order with fastballs. The inning cost him 33 pitches, a few hitting 97 and 98, but he didn’t falter until Culberson homered in the sixth.

That was enough to tie the game once Newcomb (one run over six innings) settled down. The Nationals managed to put multiple runners on base once against him, in the fifth inning, but Soto struck out looking at a borderline 3-2 curveball to quash the threat.

“This was a big league juego,” Scherzer said, using the Spanish word for game. “Everybody was out there grinding, and it just happens that they won.”

The day began with Rodriguez surpassing expectations to earn his first career win. The lanky right-hander allowed one run on three hits in five innings. He peppered the strike zone — not his forte — and threw just 64 pitches because Martinez decided to pull him before he faced Atlanta’s potent lineup a third time. He mixed his change-up more than in his previous five major league outings and avoided the inevitable pitfalls that plague a two-pitch starting pitcher. In between, he smacked a two-out double for his first career hit during the Nationals’ four-run fourth inning.

“I’m very excited, very emotional, obviously,” Rodriguez said. “That’s what we work hard to accomplish. And now that I did, I’m very excited.”

The Nationals caught a break when Spencer Kieboom whacked a 104-mph line drive that deflected off Braves starter Max Fried in the second inning. Fried recovered to throw Kieboom out for the final out of the frame, but he didn’t throw another pitch. He was later given a diagnosis of a strained groin, a product of him attempting to avoid the comebacker rather than the comebacker’s actual impact, and placed on the disabled list after the game. His exit left the Braves in a predicament, needing to turn to the bullpen by the third inning. It cost them.

Kolby Allard, another left-hander, was summoned in relief and succumbed in the fourth inning. The blitz began with Harper launching a 113-mph missile over the right field wall for his 27th home run. Ryan Zimmerman followed with a blast to straightaway center, giving Washington its second pair of back-to-back home runs this season.

Two batters later, Kieboom, owner of a .211 batting average, walked to extend the inning for Rodriguez, who doubled down the left field line. Trea Turner and Soto then followed with RBI singles. The Nationals supplied another four-run frame in the sixth inning on three walks and two hits, including an opposite-field RBI single from Harper and Zimmerman’s two-run double. Zimmerman finished the day 6 for 8 with a home run, three doubles and a walk.

“Since I’ve come back I feel like I’ve had good at-bats, hit the ball well,” Zimmerman said. “My body’s now starting to feel good back in there playing a lot more than I was when I first came back.”

Rodriguez started the game as Washington’s 26th man for the doubleheader, meaning the club didn’t have to make a roster move to accommodate him. The Nationals were sending him back to Class AAA Syracuse after the first game regardless of the outcome. With Scherzer slated to start the nightcap, Martinez said he was “ready to do different things” with his bullpen to secure the 27 outs if necessary. Nothing beyond the ordinary, however, was needed. Five relievers combined to log four innings, including Greg Holland, who struck out three in his Nationals debut.

The performance left the Nationals in prime position for a sweep they weren’t supposed to have a chance to complete. They threatened to come back in the ninth inning of the second game, putting runners on first and second with one out. But Wieters lined into a double play to end the game and a day that began with so much promise.