"It went well," said Harrison, who had back surgery on June 3, 2014. "I made a big jump in my velocity. I made an adjustment with pitching coach Brad Holman and I could tell a huge difference how the ball was coming out of my hand."
Harrison will likely need 2-3 more starts before he is an option at the big league level. But he is convinced that he is going to make it all the way back from a spinal injury that appeared to be career threatening.
"At this point I need to get my command down," Harrison said. "If I can hone in on what I had the last game, I'm very close."
Perez is expected to follow Harrison in the Round Rock rotation and pitch either Monday or Tuesday. His first start was promising as Perez threw 45 pitches over 2 2/3 innings for Double-A Frisco on Wednesday, allowing one run on five hits, no walks and four strikeouts.
"I feel great, my arm is good, my body is good," Perez said. "I just want to continue to do what I need to do and get ready 100 percent. There has been no pain and no soreness. I feel like I have a new arm."
Perez, who is coming back from Tommy John surgery, is expected to throw 60 pitches in his next start. He could be 3-4 starts away from being an option at the Major League level.
Right now there is no room in a rotation of Yovani Gallardo, Colby Lewis, Nick Martinez, Alex Gonzalez and Wandy Rodriguez. Those five have a combined 2.26 ERA in their last 13 games.
Manager Jeff Banister said one possible solution is a six-man rotation.
"I have considered a six-man rotation to be a viable option," Banister said. "In today's baseball it's something you should look at with the injuries, innings and number of pitches."
T.R. Sullivan is a reporter for MLB.com. Read his blog, Postcards from Elysian Fields, follow him on Twitter @Sullivan_Ranger and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.