Ross Ohlendorf landed on the DL over the weekend. (Doug Pensinger/Getty Images) Ross Ohlendorf landed on the DL over the weekend. (Doug Pensinger/Getty Images)

The Nationals selected the contract of right-hander Tanner Roark from Class AAA Syracuse and optioned left-handed reliever Xavier Cedeno, a move to fortify the pitching staff while Ross Ohlendorf remains on the disabled list.

Ohlendorf landed on the disabled list with right shoulder inflammation over the weekend after tossing only 15 pitches on July 31 because of a tired arm that hadn’t recovered from his previous appearance, a 114-pitch start on July 26. Ohlendorf, a veteran, had pitched brilliantly since being brought up to Nationals, punching up a 1.85 ERA over 34 innings as a long reliever and spot starter. He was the prime candidate to take over rookie right-hander Taylor Jordan’s spot in the rotation when he was shut down later this month in his first full season back from Tommy John surgery.

Ohlendorf’s tired arm complicated matters. He could still return in two weeks and replace Jordan in the rotation, but in the meantime the Nationals wanted to bring up an extra arm to take his place. The Nationals first turned to Cedeno, who didn’t appear in a game in this stint, but now called up Roark, who is perhaps best equipped to fill Ohlendorf’s shoes.

Roark, 26, posted a 3.15 ERA and 9-3 record over 105 2/3 innings with Syracuse this season. He started 11 games and appeared as a reliever in 22 others. He also has two saves and four holds. He has a 0.994 WHIP (best in the International League), a strong 4.20 strikeout to walk ratio and opponents hits .217 off him (tied for first in the International League). Roark started off the season slow but has a 2.05 ERA and 6-0 record over the past 10 starts and has walked only four batters over those 52 2/3 innings.

Roark throws a mid-90s fastball with a sharp curveball and “very good change-up,” according to Syracuse pitching coach Greg Booker. Roark could serve as a long reliever or even take Jordan’s spot in the rotation should Ohlendorf need more time to recover.

“(Roark has) thrown extremely well and he’s kind of a hybrid between a long reliever and starting pitcher so he brings some versatility to the organization and another quality arm,” General Manager Mike Rizzo said of Roark on Monday.

In order to make room for Roark on the 40-man roster, the Nationals transferred injured left-handed starter Ross Detwiler from the 15-day disabled list to the 60-day disabled list. Detwiler has been on the disabled list with a herniated disk since July 4. The Nationals hope that Detwiler could be ready to return in September, but are also aware of the possibility that the he may miss the rest of the season.

Roark was acquired in a July 2010 trade that brought him and fellow Syracuse pitcher Ryan Tatusko to Washington in exchange for sending infielder Cristian Guzman to the Texas Rangers, another victory of a minor trade executed by Rizzo. After 15 games with Texas, Guzman never played in the majors again.