Smoltz allowed four hits and one run, walking none and striking out six. He threw 73 pitches, 52 for strikes.
Barring any setbacks, Smoltz is expected to move up to Triple-A Pawtucket for his next two starts and then join the Red Sox.
This was the third rehab start for Smoltz, who had right shoulder surgery last June when he was with the Atlanta Braves.
"I felt really good," said Smoltz after the outing. "And for the most part, I tried to establish my fastball. I had a cranky beginning, but it worked itself out and I got into a nice little groove."
The Red Sox look forward to Smoltz getting in that kind of groove for them.
"I think I'm going to get a little more complete each time," Smoltz said. "For the most part, I'm really pleased with today's effort. I felt really fresh in the fifth inning, even though it's the longest stint I've had."
In his three rehab starts, Smoltz has a 1.59 ERA. He has displayed his trademark control, walking none and striking out 10 over 11 1/3 innings.
Ian Browne is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.