Bryce Harper has another rough outing against the Orioles, going 0 for 5 while hitting from the No. 2 spot in the order. (Greg Fiume/GETTY IMAGES)

At first, Ross Detwiler didn’t look as Nick Markakis’s two-run home run in the fifth inning sailed toward the right field seats. He then did, the shoulders of his lanky 6-foot-5 frame slouched, arms at his sides, his face sporting an utterly blank stare as he looked out into those same stands. Hours after his place on the pitching staff seemed solidified Saturday, his start was coming unraveled.

On the day he received the most public vote of confidence from Washington Nationals officials that he would remain in the starting rotation when injured Chien-Ming Wang returned from the disabled list, Detwiler delivered his worst performance of the season. The 26-year-old allowed six runs on nine hits, including a pair of two-run home runs, in a 6-5 loss to the Orioles before an announced crowd of 42,331 at Nationals Park.

“Give up six in five innings? That’s awful,” Detwiler said.

Some 470 miles northwest of Washington, the pitcher who was at first considered Detwiler’s rotation replacement was on the mound. Wang, whose rehab schedule coincides with Detwiler’s starts, was pitching in Toledo, Ohio, for Class AAA Syracuse. It was the fifth start of his 30-day rehab assignment from a strained right hamstring. That stretch ends in a little more than a week, and for some time, the two pitchers’ success has puzzled Nationals officials on what to do.

The likely option before the season was to send Detwiler to the bullpen and give his spot to Wang. But entering Saturday’s game, Detwiler was a vital part of a Nationals’ starting rotation that was the best in baseball. He sported the fourth-lowest ERA (2.75) of the Nationals starters, which, compared to the rest of the National League, was among its top 25 starters. The first-round pick from the 2007 draft was showing that the fifth spot in the rotation he surprisingly earned over the more established John Lannan in spring training was indeed his to keep.

And because of that, Manager Davey Johnson and General Manager Mike Rizzo both revealed on Saturday that when Wang is ready to return, he likely will head to the bullpen and Detwiler probably will retain his spot in the rotation — at least for now.

It took the Orioles (27-14) only until the second inning to solve Detwiler. Then the scoring came in two-run chunks for the left-hander. After a leadoff single to Wilson Betemit and a five-pitch walk to Xavier Avery, leadoff hitter Robert Andino drove in two runs with a single to left field.

An inning later, Adam Jones, a thorn in the Nationals’ side already this series, showed a big reason why the Orioles are surprisingly in first place in their division by slamming a Detwiler fastball so hard it went over the visitor’s bullpen in left field and landed in the seats behind it.

Two innings later, Markakis, author of Friday night’s winning home run, hit a two-run homer to right-center field that elicited “Let’s Go O’s” cheers from the stands. That was Detwiler’s last inning and the first time since Sept. 10, 2011 that a Nationals starter had allowed six runs. And those six runs were too much to overcome.

“I know I’m here for a reason in this role,” Detwiler said. “It’s like, you just kind of have to take it for what it is and go after the next one. Tonight, I’m going to let it sink in a little bit. I feel terrible about it because our team was out there, the hitters were ready to hit. They put up five runs on that pitching staff which, we need to win when we do that.”

With the Nationals’ offense sputtering as it has, any weakness in pitching can be magnified. A starter’s average or bad night can turn into a headache when hitters fail to turn opportunities into runs. On Saturday, the Nationals’ offense — despite tweaks to the lineup from Johnson — didn’t show any spark until the sixth inning.

“We’ve been doing that a lot this year, just not getting out to good starts,” Nationals first baseman Adam LaRoche said. “The five, six innings with a couple hits and not scoring.”

In the sixth, Nationals hitters produced three runs and chased Orioles right-handed starter Jason Hammel, who had befuddled Nationals hitters from the start, allowing only two base runners through four innings. Two runs scored on a double to left-center by Rick Ankiel. Catcher Carlos Maldonado, making his first start of the season since being called up four days earlier because of a rash of injuries, plated a run with a groundout and Roger Bernadina added the inning’s third run with a single up the middle.

The Nationals (23-17) put the tying run on first base with one out in the bottom of the eighth inning, but the opportunity was killed with consecutive flyouts by Bernadina and pinch hitter Danny Espinosa.

Ryan Zimmerman added a full-count, two-out solo home run in the ninth inning to trim the deficit to one run. But Orioles closer Jim Johnson struck out LaRoche with a full-count fastball to end the game. And with that, any chance of ending Detwiler’s difficult outing with a win was squandered.