On his return to duty, Ricketts was assigned to command of a division in Irvin McDowell's corps, which he commanded at the Battle of Cedar Mountain, where he covered Nathaniel P. Banks's withdrawal. At Second Bull Run, his division was thrown forward by McDowell into Thoroughfare Gap to bar the advance of James Longstreet, who was seeking to unite his wing with that of Stonewall Jackson. Ricketts, who was being flanked and in danger of being cut off, withdrew. At the subsequent Battle of Antietam, he had two horses killed under him and he was badly injured when the second one fell on him. When he recovered sufficiently for duty, he was appointed to the Fitz John Porter court-martial. The trial was created to convict, with every judge beholden to Edwin M. Stanton for tenure or impending promotion except for Benjamin M. Prentiss. Ricketts probably voted for acquittal and was not promoted.