Afterward, Walker said his shoulder felt good and that he's ready to embark on his second rehab assignment of the season.
"I didn't get tired at the end," he said. "I felt like I was strong. I could have gone another inning or so ... everything was game-mode. I wasn't trying to hold back or anything. I was just going right after them."
The Mariners haven't given official word on when or where Walker will be sent in their Minor League system. They also haven't specified how long his rehab stint will last. Walker went 1-0 with a 3.60 ERA last year in three starts during a late-season callup, but he hasn't pitched in the Major Leagues in 2014 while dealing with the shoulder problems.
In late February, the club shut him down for a week when it discovered inflammation in the bursa sac of his right shoulder. He rehabbed during Spring Training and made his season debut in early April with Class A High Desert, allowing four hits and two runs, one earned, in 4 1/3 innings. Then, he was promoted to Double-A Jackson, where he struck out 10 in five shutout innings, giving up three hits in his only appearance with the Generals.
By mid-April, Walker was arguably one step from rejoining the rotation, but he was scratched a few hours before his rehab start with Triple-A Tacoma after complaining of shoulder stiffness. Afterward, he was diagnosed with the impingement.
"I felt like I was right there ready to go, and then I was going to head back up here," he said. "But I just stayed positive. I was able to get ready, get out there and get my work done without being down about it."
Walker said he's altered his mechanics so that it sometimes feels like he's "walking up to the plate" when he finishes his delivery. Following through on his pitches, he said, can relieve the pressure on his shoulder.
"I definitely feel like after I pitch a game it won't be as sore as it usually would because I'm using my legs and finishing, so I'm taking all that stress off my arm," he said.
Adam Lewis is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.