Garza went 4 2/3 scoreless innings, allowing four hits and walk while striking out two.
"[Garza] looked really good," Maddon said. "I really liked his fastball today. He pitched primarily with his fastball. ... Philosophically, I like that."
"I felt good," Garza said. "We had some stuff we've been working on from the past start, mechanically. It's not there completely, but getting there. [I'm] getting more consistent with my pitches and being able to do things."
In his three starts this spring, Garza has faced the Tigers, Yankees and Red Sox.
"I think it's a good thing for us to see," Maddon said. "Every start is a competitive situation, but I think every time out, he's gotten better, and you can see where he can compete against this very good [Sox] lineup. I like the steady improvement from what we've seen the first time out."
Garza gave way to the lefty Howell in the fifth with two outs, a runner on first base and left-handed hitting Alex Cora coming up. Howell allowed a single up the middle to Cora, but got the next batter, Jacoby Ellsbury, to ground out to Carlos Pena at first.
Howell went 2 1/3 innings, allowing a run on two hits and a walk.
"Part of that is just to stretch him out, and the other part is to see how he looks in that [situational lefty] role," Maddon said. "Every time he's come out this spring, he's pitched extremely well. I think there's a confidence he has about this role. I think he likes it.
"He's a competitive guy. You feed off his energy. When you see him in the dugout, he's an energetic guy. The team likes to play behind him because he's going to throw strikes and he works fast. He's done a nice job."
Maureen Mullen is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.