Correction: The article incorrectly referred to Baltimore Orioles pitcher Jake Arrieta as a left-hander. He bats and throws right-handed. This version has been corrected.

Ian Desmond walks off the field after getting tagged out at second base for the final out of the game. (Toni L. Sandys/The Washington Post)

It’s tough to fault Nationals reliever Sean Burnett too much for the fastball that was too high to Orioles catcher Matt Wieters in the eighth inning of a one-run game Sunday afternoon. For all the jumbled roles the Nationals’ bullpen has endured because of injuries, Burnett has been a steady force, a left-handed reliever who has made the eighth inning carefree for Washington.

Burnett gave up a single to Adam Jones and then a decisive two-run home run to Wieters in a 2-1 loss to the Orioles. But he, the Nationals’ starting pitching and the team’s bullpen have propelled the franchise’s rise to first place in the National League East. That status has been achieved despite one of the lowest-scoring offenses in the major leagues that leaves little room for error in tight games.

“It’s not the easiest thing in the world,” said Burnett, who admitted he made a bad pitch to Wieters. “You’d like to have a little bit of leniency.”

The Nationals scored their only run of the day — and on most days, a one-run lead has been enough — when slumping Ryan Zimmerman, the cornerstone of the franchise, drove a pitch into left field for an RBI single in the third inning.

An hour before game time, Zimmerman received his second cortisone shot in two months for pain in the inflamed AC joint of his right shoulder. The nagging discomfort, caused by several diving plays in the field, hasn’t affected Zimmerman’s fielding. In the fifth inning, with two runners taking off on a double steal with one out, he made a nifty grab of a tough groundball and threw across the diamond while on the run for a crucial out.

“He is playing third base better than anybody,” rookie outfielder Bryce Harper said.

But the pain has derailed Zimmerman’s hitting. It has sent him spiraling into a vicious slump, the worst of his career. Doctors agreed to give him a cortisone shot before the game.

Little-used backup catcher Jhonatan Solanoled off the third inning with a double into the right field corner, his third extra base hit in only his 14th at-bat of the season. Steve Lombardozzi was hit by a pitch and Solano advanced to third base when Harper grounded into a double play, his first in 213 major league plate appearances. Zimmerman strode pain-free to the plate with a chance to give the Nationals a lead with two outs. On a 3-1 pitch, he smacked a sharp line drive into left field for a single and his first RBI in 12 games.

Zimmerman added another single, finishing 2 for 4, his first multi-hit game since June 8.

“He looked like the old Zim,” said Manager Davey Johnson, who has stuck with Zimmerman in the heart of his batting order despite the third baseman’s struggles.

But the Nationals managed only six hits against the Orioles. Harper notched two, including a crowd-rousing hit to center field in the sixth inning that he stretched into a double with his usual aggressiveness. Only twice, though, did the Nationals have multiple base runners in an inning.

The Nationals have become accustomed to playing one-run games and are 14-12 in them after Sunday’s loss. With more than a third of their contests nail-biters, there is more pressure on their standout pitching to carry them.

Against the Orioles this weekend, the Nationals scored only five runs in three games. Facing shaky starter Jake Arrieta, a right-hander who entered the game with a 5.83 ERA, they managed only one run on five hits. Three Orioles relievers held the team to one hit over the final three innings.

While Sunday’s loss wasn’t a result they wanted, the Nationals finished the toughest stretch of their season so far in first place in their division. Over the past month, they have played 32 games against arguably the best two divisions in the sport, the AL East and NL East. Seven of the nine teams they faced had winning records when the series began. They finished the swing with an 18-14 record.

“I don’t think anyone is too upset,” shortstop Ian Desmond said. “We would like to walk out of here with a series win, but we’ve been playing pretty good baseball. It’s pretty tough to hang your head after a loss like this.”

Left-hander Ross Detwiler, making his first start since he was re-inserted into the starting rotation, threw aggressively and allowed only four weak hits over five scoreless innings. When he ran into trouble and a tight strike zone in the fourth and fifth innings, he induced two warning-track flyouts to strand five runners.

Reliever Craig Stammen pitched two scoreless innings in relief before handing the ball to Burnett in the eighth, a spot where he has excelled. But with one pitch to Wieters, the Nationals’ fortunes turned instantly.

“I can’t take offense with [Burnett],” Johnson said. “He’s been almost perfect every time out.”

“We need to score more,” Zimmerman said. “That’s not a question. Those guys have been unbelievable. [Burnett] has been right there at the top with those guys, and he’ll be right there tomorrow, I’m sure. We want to score more runs.”