Smoltz gave up a leadoff homer in the third to Keith Ginter of the Charlotte Knights on a 91 mph pitch Wednesday night.
The 42-year-old right-hander yielded three hits and a walk with two strikeouts on 61 pitches, 36 for strikes. He left his sixth rehab appearance trailing 1-0 and is slated to make his first start for Boston next Thursday at Washington.
The only pitcher with at least 200 wins and 150 saves had shoulder surgery on June 10, 2008. The Red Sox signed Smoltz in January to a one-year, $5.5 million contract after he spent his first 20 seasons with Atlanta.