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5/28/2014 8:04 P.M. ET

Rangers acquire Irwin for Triple-A rotation

MINNEAPOLIS -- The Rangers acquired pitcher Phil Irwin off waivers from the Pirates to help reinforce their tattered Triple-A rotation at Round Rock. The Triple-A pitching depth has taken some big hits because of the Rangers' injuries at the Major League level.

Career reliever Cory Burns had to make his first professional start last Sunday and Miles Mikolas is tentatively scheduled to make his first start on Friday.

Irwin was the Pirates' 21st-round pick in the 2009 First-Year Player Draft and rising through their system until missing almost all of last season because of a nerve injury in his right elbow that required transposition surgery. Irwin, who made one start for the Pirates in 2013, was 1-2 with an 8.72 ERA in 10 games at Triple-A Indianapolis.

"He has been 89 to 92 miles per hour with his sinker and he has always had a good curve ball," said Josh Boyd, the Rangers' director of professional scouting.

Poreda odd man out in bullpen, sent to Triple-A

MINNEAPOLIS -- Left-handed reliever Aaron Poreda was the victim of rules, circumstances and numbers. The Rangers had to send him back to Triple-A Round Rock on Wednesday to make room for Joe Saunders, who was activated off the disabled list.

Poreda was 2-0 with a 3.38 ERA in 15 outings for the Rangers. In 13 1/3 innings, he had allowed 15 hits, four walks and 11 strikeouts. But he has options, meaning he can be sent to the Minor Leagues without being put through waivers. The Rangers also had two other left-handers in the bullpen in Robbie Ross Jr. and Neal Cotts.

"Those are the toughest ones to deal with because you don't have any reason to tell them," manager Ron Washington said. "He was a class act. He understood. He's going to go down there and keep throwing."

Poreda, a former No. 1 Draft pick out of the University of San Francisco by the White Sox, still has a chance to be a major success story for the Rangers. He was signed as a Minor League free agent this winter after missing almost two complete seasons because of Tommy John surgery and appears to be back at full strength. His fastball has averaged 94.9 miles per hour, the highest on the staff.

"I have been very pleased," Poreda said. "My fastball command has been great and my walks are way down. That was my number one priority, having the command to pitch again … up and down, mixing speeds."

Robertson gives Rangers full bench

MINNEAPOLIS -- Rangers outfielder Daniel Robertson has a plastic protective mask and an enhanced batting helmet. He is an option again off the Rangers' bench for the first time since his face collided with outfielder Alex Rios' knee last Thursday in Detroit.

Robertson suffered a black eye and three small fractures in his left cheek. He will wear the clear plastic mask on defense and the special helmet at the plate. The clear plastic mask does not appear to be too obtrusive.

"I'm sweating a little bit," Robertson said. "Maybe I'll grow some facial hair and help absorb the sweat. It's fine. It's weird wearing it and frustrating wearing it but there are no limitations. If sweat is most of my problems, that's fine. For the next four to six weeks, I have to make it work."

Manager Ron Washington said he would like to get Robertson in a game as soon as possible to get him acclimated to the mask. His return gives the Rangers a full four-man bench for the first time since last Thursday. The Rangers should have five on the bench on Friday when they play the Nationals without a designated hitter.

Robertson is 3-for-20 with two walks in nine games with the Rangers since being acquired from the Padres on April 23.

Holland needs leg strength

MINNEAPOLIS -- Rangers pitcher Derek Holland went through a strenuous fielding workout on Wednesday afternoon at Target Field to test his surgically repaired left knee. The verdict is he still needs more strength and mobility in the knee before he is ready for a medical rehab assignment.

Holland is hoping that will come in the next two weeks, after the Rangers finish their current road trip and an upcoming nine-game homestand.

"The next thing is for [the Rangers] to decide," Holland said. "I don't have any say in it. It's much better but there are still some things that need to be taken care of little pushing off my back leg."

Holland, who underwent microfracture surgery on his left knee on Jan. 10, has been able to throw regularly in the bullpen without issues. The concern is being able to field his position and make tough throws pushing off his back leg. He is not able to do that right now with any consistency.

"He just has to keep working until he gets used to the new leg," manager Ron Washington said. "We're trying to get him a feel for pushing off that leg."

Worth noting

• Tanner Scheppers, on the disabled list with inflammation in his right elbow, made his second appearance on a rehab assignment Tuesday night. Pitching for Triple-A Round Rock, Scheppers pitched a scoreless inning, allowing a hit and a walk with one strikeout. He is scheduled to pitch on Thursday and again on Saturday. At that point he could be ready to be activated.

Chris Gimenez did not start on Wednesday night but now has five hits with runners in scoring position on this road trip. That's the most hits with runners in scoring position by a Rangers catcher this season.

Alex Rios started for the fifth time at designated hitter on Wednesday and Luis Sardinas made his sixth start at second base.

T.R. Sullivan is a reporter for MLB.com Read his blog, Postcards from Elysian Fields and follow him on Twitter @Sullivan_Ranger. This story was not subject to the approval of Major League Baseball or its clubs.