At daylight, Martin was attacked in the gap of Catoctin mountain which he was holding. Hampton sent up a section of Hart's battery to his support, and Martin held his position against odds until 2 p. m., the fire of Hart's guns driving the opposing artillery from several positions. Then the enemy, reinforced, gained a strong point for artillery, and Hampton withdrew Martin, and in front of Middletown formed for battle, which was soon joined. Hart's guns replied vigorously to those of the Federals, the sharpshooters became warmly engaged, and soon the whole brigade was in action, the fight being pressed by infantry on the enemy's side. Notified that Gen. D. H. Hill had taken position in Boonsboro gap, General Stuart, who had come forward, ordered Hampton to withdraw to the south, and sent Martin with Hart's guns through the gap in South mountain to Boonsboro. Hampton retired to Burkittsville, and on his way encountered a Federal cavalry command, which he charged with Colonel Young's Georgians, dispersed the force, with a loss of 30 killed and wounded on the enemy's part, and 4 killed and 9 wounded in the Cobb legion.
Hill's division, which had marched into Boonsboro gap, was composed of the brigades of Ripley, Rodes, Garland, Colquitt and Anderson. With these commands and Rosser's Fifth Virginia cavalry, Hill stood against the assaults of McClellan for five hours. Longstreet hurried back from Hagerstown to his support and arrived