In his first rehab start with the PawSox, Buchholz went 4 2/3 innings, allowing three runs, including a pair of solo shots, on four hits. He tossed 62 pitches, 42 for strikes.
"Clay went out and accomplished some of the delivery adjustments he's been working on. Overall strikes were improved," Farrell said. "Higher percentage of strikes and better power overall. He also had more defined shape to his pitches."
The right-hander has been on the disabled list since May 28 with a hyperextended left knee.
In 10 starts for Boston this season, he's 2-4 with a 7.02 ERA.
Quinn Roberts is a reporter for MLB.com. Steven Petrella is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.