Matsuzaka pitched 4 2/3 scoreless innings and allowed two hits in a 4-0 Pawtucket victory over the Rochester Red Wings. But even though he struck out four, he walked three and threw just 49 of his 87 pitches for strikes.
He topped out at 92 mph on the radar gun.
"I thought he did very well. ... I was impressed," Beyeler said. "He kept the ball down in the zone. He threw strikes. He got himself back into counts and was pretty efficient for a while.
"I was really impressed with the stuff. I saw him a couple of weeks ago in Portland, and the stuff didn't seem as crisp as what I saw tonight. I thought his slider was really crisp. He had good plane on his fastball and moved the ball in and out."
Conversely, Matsuzaka wasn't overly pleased with his performance.
"I had [three] walks and a lot of two-ball and three-ball counts, which [elevated] my pitch count," Matsuzaka said through interpreter Jeff Cutler. "I really wanted to throw at least five innings, but it didn't happen, so I'm not really happy about that."
Beyeler felt that even when Matsuzaka missed, he was close, as opposed to being wild.
"He was around the zone," Beyeler said. "It wasn't like he was missing all over the place. That's what I was looking at. There were a lot of pitches that ... looked like close pitches. A lot of the misses were down in the zone."
Matsuzaka was placed on Boston's disabled list last May 17 and underwent Tommy John surgery on June 10. Over three rehab starts, he has pitched 13 1/3 innings, allowed four runs on 11 hits, walked five and struck out 14. His ERA is 2.71.
Matsuzaka, who retired the side in order in the third on Monday, expressed concern about his surgically repaired elbow.
"Overall, my body feels good, so that's fine," he said. "But my elbow, some days it feels better than others. Right now I'm just hoping that when I start, [it's on a] day that I'm feeling good.
"Being ready [after] two more games is hard to say, because it's a step-by-step process. I'll see how I pitch in my next outing and see how that goes. Then we'll see where I stand."
Matsuzaka's next rehab start will be on Saturday, when Pawtucket hosts Columbus at 6:05 p.m. ET.
Monday's fifth inning began on a promising note, as Matsuzaka caught Pedro Florimon and J.R. Towles looking at third strikes. But Darin Mastroianni cracked a double off the fence in left-center, and Ben Revere walked.
That prompted Beyeler to remove Matsuzaka in favor of Alex Wilson, who retired Sean Burroughs on a groundout.
Matsuzaka extricated himself from jams in three of the first four innings. Rochester had runners on first and second (one reaching on an error) with two outs in the first, but Matsuzaka induced Rene Tosoni to foul out to third.
With a runner on second and two outs in the second, Matsuzaka got Towles to wave at a third strike. A runner was on second with two outs in the fourth, but Matsuzaka retired Clete Thomas on a fly ball to center.
Matuszaka doesn't feel that the layoff between his start at Portland and this outing had any impact on his performance.
"I don't think it affected how I pitched tonight," he said. "I expect to be on schedule for my next start. But I still need work. It's not perfect yet. I'll be making minor adjustments as I go along.
"Tonight I didn't discuss with the catcher what kind of pitches I wanted to work on. But I threw a lot of two-seam [fastballs], and it ended up being a good practice for that pitch."
Mike Scandura is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.