At 9 a.m. Sumner, who was accompanying the division, launched the attack with an unusual battle formation—the three brigades in three long lines, men side-by-side, with only 50 to 70 yards (60 m) separating the lines. They were assaulted first by Confederate artillery and then from three sides by the divisions of Early, Walker, and McLaws, and in less than half an hour Sedgwick's men were forced to retreat in great disorder to their starting point with over 2,200 casualties, including Sedgwick himself, who was taken out of action for several months by a wound.^[21] Sumner has been condemned by most historians for his "reckless" attack, his lack of coordination with the I and XII Corps headquarters, losing control of French's division when he accompanied Sedgwick's, failing to perform adequate reconnaissance prior to launching his attack, and selecting the unusual battle formation that was so effectively flanked by the Confederate counterattack.

The final actions in the morning phase of the battle were around 10 a.m., when two regiments of the XII Corps advanced, only to be confronted by the division of John G. Walker, newly arrived from the Confederate right. They fought in the area between the Cornfield in the West Woods, but soon Walker's men were forced back by two brigades of Greene's division, and the Federal troops seized some ground in the West Woods. The morning phase ended with casualties on both sides of almost 13,000, including two Union corps commanders.