This was the first game action for Lackey since April 6, when he strained his right bicep in a game against the Blue Jays.
He will need at least one more Minor League start before he is ready to rejoin the Red Sox.
Lefty relievers Craig Breslow and Franklin Morales are also on the rehab trail this week. Breslow will pitch on Tuesday for Portland. Morales, who is being stretched out as a starter, pitched on Wednesday night at Portland.
The original schedule had Morales piggybacking Lackey on Monday, but that changed when Morales had some soreness in his left pectoral muscle.
Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, and follow him on Twitter @IanMBrowne. This story was not subject to the approval of Major League Baseball or its clubs.