"It was more of a mechanical thing," Callaway said on Tuesday. "He wasn't using his front leg to block himself out. He was kind of landing open with his front leg and getting underneath the ball. So, he had no power. What he does best, when he's going good, is he blocks himself off with that front knee and he throws through it and drives his hips through it. He just wasn't doing that on Sunday."
During his Opening Day outing against the A's on March 31, Masterson turned in seven scoreless innings with four strikeouts and one walk. In Sunday's no-decision, the right-hander was charged with six runs (five earned) on seven hits and ended with four strikeouts, three walks and two hit batsmen.
Callaway said the difference between the starts was the control of Masterson's two-seam sinker. The pitching coach said a weakness of Masterson's can be commanding the sinker when it has excessive movement. In those situations, rather than trying to take some velocity off the two-seamer, Callaway feels Masterson should focus more on his four-seamer.
"The problem," Callaway said, "is what he was doing mechanically, and then trying to ease up and throw strikes with his two seamer, it kind of compounded everything and made it worse. He probably should've taken the other route, drive some four-seamers in there, something that doesn't move and work off that.
"We've talked about, 'Hey, when you've got that big two-seamer that's moving a lot, let's pitch off your four-seamer and use your two-seamer for chase. If not, if you sit there and pound two-seamers that you can't control, you fall behind, you walk guys and you get beat.'"
Callaway said he and Masterson went over the issue again during the pitcher's bullpen session on Tuesday.
"It's just something he has to keep in mind," Callaway said. "He'll be fine."
Jordan Bastian is a reporter for MLB.com. Read his blog, Major League Bastian, and follow him on Twitter @MLBastian. This story was not subject to the approval of Major League Baseball or its clubs.