Gregg's brigade made contact with the leading elements of McPherson's corps on May 12. Neither commander was aware of the strength of his opponent, and Gregg acted aggressively, thinking McPherson's force was small enough his men could easily defeat it. McPherson, in turn, overestimated Confederate strength and responded cautiously. The early portions of the battle pitted two brigades of Major General John A. Logan's division against the Confederate force, and the battle was matched relatively evenly. Eventually, McPherson brought up Brigadier General John D. Stevenson's brigade and Brigadier General Marcellus M. Crocker's division. The weight of superior Union numbers eventually began to crack the Confederate line, and Gregg decided to disengage. McPherson's men did not immediately pursue.