McClernand’s advance met the enemy about five miles west of Port Gibson at Thompson’s plantation.  There was some firing during the night, but nothing rising to the dignity of a battle until daylight.  The enemy had taken a strong natural position with most of the Grand Gulf garrison, numbering about seven or eight thousand men, under General Bowen.  His hope was to hold me in check until reinforcements under Loring could reach him from Vicksburg; but Loring did not come in time to render much assistance south of Port Gibson.  Two brigades of McPherson’s corps followed McClernand as fast as rations and ammunition could be issued, and were ready to take position upon the battlefield whenever the 13th corps could be got out of the way.

The country in this part of Mississippi stands on edge, as it were, the roads running along the ridges except when they occasionally pass from one ridge to another.  Where there are no clearings the sides of the hills are covered with a very heavy growth of timber and with undergrowth, and the ravines are filled with vines and canebrakes, almost impenetrable.  This makes it easy for an inferior force to delay, if not defeat, a far superior one.

Near the point selected by Bowen to defend, the road to Port Gibson divides, taking two ridges which do not diverge more than a mile or two at the widest point.  These roads unite just outside the town.  This made it necessary for McClernand to divide his force.  It was not only divided, but it was separated by a deep ravine of the character above described.  One flank could not reinforce the other except by marching back to the junction of the roads.  McClernand put the divisions of Hovey, Carr and A. J. Smith upon the right-hand branch and Osterhaus on the left.  I was on the field by ten A.M., and inspected both flanks in person.  On the right the enemy, if not being pressed back, was at least not repulsing our advance.  On the left, however, Osterhaus was not faring so well.  He had been repulsed with some loss.  As soon as the road could be cleared of McClernand’s troops I ordered up McPherson, who was close upon the rear of the 13th corps, with two brigades of Logan’s division.  This was about noon.  I ordered him to send one brigade (General John E. Smith’s was selected) to support Osterhaus, and to move to the left and flank the enemy out of his position.  This movement carried the brigade over a deep ravine to a third ridge and, when Smith’s troops were seen well through the ravine, Osterhaus was directed to renew his front attack.  It was successful and unattended by heavy loss.  The enemy was sent in full retreat on their right, and their left followed before sunset.  While the movement to our left was going on, McClernand, who was with his right flank, sent me frequent requests for reinforcements, although the force with him was not being pressed.  I had been upon the ground and knew it did not admit of his engaging all the men he had.  We followed up our victory until night overtook us about two miles from Port Gibson; then the troops went into bivouac for the night.