Jeremy Hellickson suffered an injured hamstring in the first inning Sunday. (Curtis Compton/Associated Press)

Jeremy Hellickson’s cap was pulled low when he met with reporters Sunday, his voice even lower than usual as he talked about the hamstring pull that forced him from the Washington Nationals’ 4-2 loss to the Atlanta Braves after just two batters.

“That’s exactly what you didn’t want to have happen: Tanner [Roark] to have to come into that ballgame. The bullpen throws seven [scoreless innings] yesterday, and now they’ve got to get 26 outs,” Hellickson said. “It was definitely frustrating.”

That the Nationals lost Sunday’s game and the series, that they had to use seven pitchers in Saturday’s game and were therefore out of pitching Sunday, that Jefry Rodriguez had to throw 63 pitches in his major league debut three days after tossing 87 for Class AA Harrisburg, that Roark had to pitch the ninth inning three days after starting . . . none of that was Hellickson’s fault. Not really.

Because by the time Charlie Culberson took Roark deep for a two-run, walk-off homer, Washington had three hits in nine innings and would have had just one run if it weren’t for an error. By the time Culberson sent the Nationals to a series loss against their division rivals, sent them home 1½ games behind the first-place Braves in the National League East, they had scored nine runs in that time — or fewer than two per nine innings. They had compiled 19 hits — or four per nine innings. They had struck out 44 times.

“In big moments, we’ve asked for them to put the ball in play,” Washington Manager Dave Martinez said. “We struck out a few times in big moments today. Unfortunately, we couldn’t score those runs.”

Jefry Rodriguez became the 42nd player used by the Nationals this season, tied for most in the majors. (Daniel Shirey/Getty Images)

The reasons for the trouble are many, and they are not easily remedied. First of all, Sunday’s lineup included three players from the Opening Day lineup. Matt Adams fouled a pitch off his foot Saturday and could not start Sunday. His status is unknown. On the day that Martinez acknowledged Daniel Murphy might not be ready anytime soon, the manager also had to give Bryce Harper just his second day off of the season. The last thing he needs is for his healthy stars to get run down, too. Harper struck out looking as a pinch hitter in the eighth. His absence didn’t help.

But even with Harper in the lineup over the weekend, the Nationals sputtered. The only runs they scored Sunday came when Wilmer Difo reached on an error and Trea Turner homered to left-center to score him. The only other time they threatened was in the ninth, when they put runners on first and second with no one out thanks to Juan Soto’s walk and a bloop hit from Anthony Rendon.

Soto failed to tag up on Mark Reynolds’s line drive to center, but even if he had reached third with fewer than two outs, the Nationals’ next two hitters did not produce results that would have scored him. Brian Goodwin struck out looking, and Michael A. Taylor struck out swinging.

“I feel like we’ve missed a lot of pitches lately. I know I have,” Turner said. “Me and Tony [Rendon] talked about it. He feels the same way. I think it’s a matter of not missing those pitches and continuing to compete.”

Instead of handing Sean Doolittle a lead to end the game there, the score stayed tied until the ninth, forcing the Nationals to go to Roark. After Saturday’s marathon, they had only Doolittle and Wander Suero left.

Roark was able to throw an inning — he skipped his between-starts bullpen session Sunday — but no more. Martinez had to save Doolittle for a lead. He didn’t want to use Suero until he had used all other options, figuring Suero could provide the most length and not wanting to be forced to pinch-hit for him in some key moment.

So Roark came in, and he left a pitch up to pinch-hitter Culberson, who drove home just the second and third runs the Nationals’ bullpen surrendered in 15 2/ innings over the past two days. If a starter had allowed three runs in 15⅔ innings, he would have put together two strong starts. After Justin Miller provided a herculean showing Saturday, Rodriguez did the same in his major league debut.

Rodriguez is 24, to this point most known to casual fans for his suspension last season for performance enhancing drugs. To those within the Nationals organization, he is a promising starting prospect, a hard-throwing right-hander who isn’t their most big league-ready but soon could be knocking on the door. They did not expect to need him this soon.

But after Hellickson went down with a hamstring injury, one that will require an MRI exam Monday before any disabled list decisions, Rodriguez made his major league debut with one out in the first inning and faced Freddie Freeman. He needed one pitch to retire him. Though he allowed Hellickson’s base runner to score, he allowed the Braves nothing more, scattering four hits and three strikeouts over the first 4⅔ innings of his career.

Thanks to Rodriguez, Miller and many others, the bullpen held the Nationals in this weekend’s games, keeping them close inning after inning as the offense couldn’t score. That bullpen held them in the game after Hellickson went down. And in the end, that bullpen — represented by starter Roark — surrendered the decisive runs, forced into that situation because the offense couldn’t score nearly enough of its own.