OAKLAND, Calif. -- The A's shuffled their rotation and their bullpen Friday, making four roster moves.

Struggling right-hander Dan Straily, the No. 4 starter, was optioned to Triple-A Sacramento, and left-hander Drew Pomeranz moved from the bullpen into the rotation.

In other moves, right-handed reliever Ryan Cook was placed on the 15-day disabled list with a right forearm strain, while left-hander Fernando Rodriguez and right-hander Joe Savery were called up from Sacramento to bolster the bullpen.

Straily went 1-2 with a 4.93 ERA and allowed nine home runs in seven starts.

"Just needs to work on refining fastball command, getting ahead of guys," manager Bob Melvin said before the A's 8-0 victory Friday night against Washington. "We've seen him have success here before and just hasn't been as consistent, so therefore we felt the best avenue for him is to go down and work on things with less pressure than you get at the big league level. Still a guy we expect big things out of."

After making nine relief appearances this season, Pomeranz made a spot start Wednesday in the second game of a doubleheader against Seattle. He threw five shutout innings, striking out five, walking none and allowing just two hits in a 2-0 victory.

"Really excited," Pomeranz said. "I feel great. Good to go."

The 6-foot-5, 240-pound Pomeranz struggled as a starter for most of the previous three seasons with Colorado before being traded to Oakland in December in the Brett Anderson deal. But he said he recaptured his curveball this year, and Melvin said his command is much better than it was with the Rockies.

"We've seen it since he's been here," Melvin said. "We saw it in the spring. A guy that in the past has had a little trouble throwing strikes, but that hasn't been the case here. Has a plus fastball and a plus breaking ball, used his changeup a little bit in the starting role the other day and has pitched his way into this role. It's difficult to be that long (reliever), too. You're not getting regular work, but each and every time we called on him he's done a good job for us -- and certainly in a starting role as we saw the day before yesterday."

Cook left the first game of the doubleheader in the 10th inning after feeling tightness in his right forearm. An MRI on Thursday showed no damage to his elbow ligaments and nothing to indicate he would need Tommy John surgery.

"The diagnosis was nothing more than a forearm strain," Cook said. "It's not anything serious. The MRI came back and said my UCL and everything looked great. So nothing like that. Strictly a forearm strain and it shouldn't be that long."

Cook will be shut down until he's pain-free.

Rodriguez came to the A's from Houston in February 2013 but underwent Tommy John surgery on March 27 that year and missed the season. In 11 relief appearances for Sacramento, he was 1-0 with a 0.73 ERA, 11 strikeouts and four walks. He made his A's debut Friday night, pitching a scoreless ninth.

"It's been a long year, but at the same time it feels like it's just been a few days ago that I was here doing my rehab," Rodriguez said after the game. "Just excited to help the team finally. That's one of the biggest things I always thought of when I was doing my rehab."

With Pomeranz moving to the rotation, Savery gives Oakland another left-hander in the bullpen. They claimed Savery off waivers from Philadelphia on Feb. 17. He went 4-0 with a 3.86 ERA and 14 strikeouts in 11 2/3 innings of relief for Sacramento. In 41 appearances for the Phillies from 2011 to 2013, he went 3-2 with a 4.15 ERA.

"When you get sent down, you never know if you're coming back," Savery said. "There's always the chance you toed the rubber for the last time. Just thankful and glad that I get an opportunity to be back."