Penrod allowed two runs on three hits and struck out seven over 2.2 innings for Triple-A Worcester on Friday.
Penrod, who had been sidelined since June 6 with a leg injury, started for the WooSox but was not given a long leash in his return. He fanned six of the first seven hitters faced before allowing runs in his third and final frame. The 27-year-old left-hander, whom the Red Sox signed out of independent ball last season, could be a bullpen option for Boston down the stretch.