Weitzel, as has been said, took transport on the 9th of July immediately after the formal capitulation. Getting under way toward evening, he landed at Donaldsonville early the next morning. His presence there so threatened the flank and front of Taylor's forces, as to induce an immediate withdrawal of the guns from the river and the calling in of all detachments. Morgan, with Grover's First brigade and Nims's battery, followed Weitzel about midnight on the 10th, and Grover himself, with his other two brigades, on the 11th. During the night of that day, Grover therefore found himself before Donaldsonville, holding both banks of Bayou La Fourche with two divisions. He was confronted by Green with his own brigade and Major's, together with the batteries that had lately been annoying the transports and drawing the attention of the gunboats on the river. When, on the 10th, Green saw the transports coming down the Mississippi laden with troops, it did not at once occur to him that Port Hudson was lost; he simply thought these troops were coming to attack him. Concentrating his whole force, he posted Major with four regiments and four guns on the left or east bank of the bayou, and on the right or west bank three regiments and two guns of his own brigade. Green's pickets were within two miles of Donaldsonville. As Grover developed and took more ground in his front, Green drew back toward Paincourtville.
On the morning of the 13th of July, without any intention of bringing on a battle or of hastening the enemy's movements, but merely to gain a little more elbow-room and to find new fields for forage for his animals, Grover moved out an advance guard on either side of the bayou. "The enemy is evidently making preparation," he said in his despatch of the 12th before ordering this movement, "to escape if pursued by a strong force or to resist a small one. Our gunboats can hardly be expected at Brashear City for some days, and it is evidently injudicious to press them until their retreat is cut off." Dudley, with two sections of Carruth's battery under Phelps and with Barrett's troop, marched on the right bank of the bayou, supported by Charles J. Paine's brigade with Haley's battery. Morgan, under the orders of Birge, temporarily commanding Grover's division, moved in line with Dudley on the opposite bank. They went forward slowly until, about six miles out, they found themselves upon the estate of the planter whose name is variously spelled Cox, Koch, and Kock. Here, as Dudley and Morgan showed no disposition to attack, Green took the initiative, and, favored by a narrow field, a rank growth of corn, dense thickets of willows, the deep ditches common to all sugar plantations in these lowlands, and his own superior knowledge of the country, he fell suddenly with his whole force upon the heads of Dudley's and Morgan's columns, and drove them in almost before they were aware of the presence in their front of anything more than the pickets, whom they had been seeing for two days and who had been falling back before them. Morgan handled his brigade badly, and soon got it, or suffered it to fall, into a tangle whence it could only extricate itself by retiring. This fairly exposed the flank of Dudley, who was making a good fight, but had already enough to do to take care of his front against the fierce onset of Green's Texans. The result of this bad mismanagement was that the whole command was in effect clubbed and on both banks driven back about a mile, until Paine came to its support; then Grover rode out, and, seeing what had happened, drew in his whole force.