Ryan Zimmerman takes off his helmet after striking out with two men on in the eighth inning. (Toni L. Sandys/The Washington Post)

The Washington Nationals arrived at Camden Yards on Monday afternoon thirsting for a long outing from their starting pitcher. They had played 10 games in 10 days through rain delays, scorching heat and extra innings, and their bullpen was gasping for air.

The burden was supposed to fall on Stephen Strasburg, but he came forward with elbow soreness over the weekend and the Nationals, ever cautious, placed him on the 15-day disabled list Monday, shifting the assignment over to A.J. Cole, who was called up to replace Strasburg on the roster.

A right-hander whose only previous major league start lasted six outs 16 months earlier, Cole delivered seven innings, more than the Nationals could have hoped for against a top-10 offense in a hitter-friendly park. But Washington’s offense, so potent recently, failed to produce when opportunities arose in a 4-3 loss.

The Nationals (73-51) struck first against Orioles right-hander Dylan Bundy, once a can’t-miss prospect, on Daniel Murphy’s first-inning RBI single. Anthony Rendon added a leadoff home run in the fourth, but Bundy was nearly flawless otherwise. Utilizing a four-seam fastball that touched 96 mph early and a slower two-seamer with movement later on, Bundy held Washington to the two runs on three hits over six innings.

“I didn’t see him do that a ton on the film,” Murphy said, “so to kind of switch up on the fly right there was impressive.”

FIll-in starter A.J. Cole finishes with a career-high eight strikeouts against the Orioles. (Toni L. Sandys/The Washington Post)

Bundy outpitched Cole, whose seven innings were a career high, surpassing a 4⅓ inning relief outing last season. Going up against baseball’s top home run hitting club, Cole’s game plan was to attack the strike zone and challenge hitters. The Orioles crushed two homers, including a moon shot by Jonathan Schoop in the third inning, off Cole, but the 24-year-old right-hander recovered to compile a career-high eight strikeouts.

“He saved our bullpen,” Manager Dusty Baker said. “He pitched a heck of a game.”

The outing completed a whirlwind for Cole. He hadn’t pitched in 11 days because he was called up to the majors to bolster the Nationals’ tired bullpen last week but didn’t enter either game he was at before he was sent back to Class AAA Syracuse on Saturday. He was slated to start Monday in Pawtucket, R.I., for Syracuse but got a call that he was needed in Baltimore.

“It’s been a weird couple days,” Cole said.

Stephen Strasburg in the dugout during the game at Camden Yards. He was placed on the 15-day DL with right elbow soreness. (Toni L. Sandys/The Washington Post)

Strasburg, Baker and General Manager Mike Rizzo echoed that the decision to shelve Strasburg is precautionary. It is Strasburg’s eighth career DL stint, but the first elbow-related setback since he tore his ulnar collateral ligament in 2010, which prompted his Tommy John surgery.

Rizzo said the team wasn’t aware of any elbow issues when Strasburg skipped the All-Star Game, and he is confident Strasburg’s elbow is structurally sound, though Strasburg hasn’t undergone an MRI exam since he disclosed the soreness.

“I don’t think we’re at the MRI stage right now,” Rizzo said. “If we did, it would just be a precautionary one, just to get another image. We have one from when he signed his extension [in May], so we have a fairly current one. And we feel we have our arms around what’s going on there.”

Strasburg acknowledged Monday that he had been steadily losing flexibility since the all-star break, and recovering between starts became a challenge. He added that, as a Tommy John surgery recipient, he is constantly learning how to navigate a season. He indicated he will change his workout routine between starts to focus more on flexibility when he returns.

Until then, the Nationals will have another vacancy in their rotation. On Monday, Cole filled it and pitched like the promising prospect he once was — even without the velocity he once boasted — besides a three-run blitz in the fourth inning.

The sudden barrage began when Manny Machado launched a rocket off the left field wall. An accurate throw from Ben Revere would’ve been on time to get Machado at second base, but Revere misfired and Machado slid in safely with a double. Chris Davis then smacked a line drive to right field where Bryce Harper bobbled the ball, allowing Machado time to score to tie the game and Davis to reach second for another double.

Two pitches later, Mark Trumbo crushed a 92-mph fastball over the left field wall, his 38th home run this season. Trumbo’s past seven hits have all been homers. The Orioles didn’t square Cole up again.

Baltimore kept hitting the ball in the air, but the connections hung. Cole retired 12 of the final 14 batters he faced — seven on popouts or flyouts — to get through seven innings, an unexpected gift for an exhausted bullpen. But the Nationals, which had scored 77 runs over the previous seven games, failed to generate the offense to capitalize.

Danny Espinosa, a dead pull hitter, went opposite field to register his first home run since July 3 to lead off the seventh inning against Mychal Givens and cut Washington’s deficit to one. Murphy then began the eighth with a double off sidearmer Donnie Hart, but Murphy was caught off the bag on Harper’s grounder up the middle and tagged out.

Rendon later walked with two outs, and the runners advanced to second and third on a wild pitch to Ryan Zimmerman. In his third game back from the disabled list, Zimmerman engaged in a battle with the hard-throwing Brad Brach but struck out swinging on the seventh pitch, a splitter down out of the strike zone. It was the second time the Nationals led off an inning with a double and failed to score, sealing a missed opportunity to steal a victory.

“We’ve certainly got to get better, because we take pride in winning those one-run games,” Baker said. “Like we said in spring training, the team that wins one-run games is usually the one that’s out in front and stays out front. This is what it’s going to be kind of like in playoff baseball.”