Rebel skirmishers are taking advantage of every twist and turn in the narrow road to delay Grant’s advance; at Grindstone, Hankinson’s ferry and the crossing of the Big Black River. But they are only covering Bowen’s evacuation from Grand Gulf. When they set off the fort's powder magazines Grant hears the explosion while on the road from Port Gibson and knows what it means.
That evening Marines from Admiral Porter’s river squadron occupy the town. Grant arrives shortly thereafter to get a bath and receive communications. It is here that he receives a letter from Sherman warning him not to attempt to supply his army down the single road Sherman’s men are now following to Grand Gulf. “…stop all troops till your army is…supplied with wagons, and then act as quick as possible; for this road will be Jammed, as sure as life." It is also here that Grant learns that because of Confederate activity General Banks does not anticipate bringing siege against Port Hudson for another two weeks.
Grant’s original plan was to capture Port Hudson and establish that as his new supply base, and perhaps Grant could then borrow a corps of men from Bank’s command to assist in his attack on Vicksburg. But with Bank’s delay Grant decides he must come up with a new plan on the run. But now he also has in hand Grierson’s initial report of his Mississippi raid, containing the key phrase; “The Confederacy is hollow”. Grand decides to gamble. He will cut himself loose from any base and risk taking on Pemberton with only his own troops. He tells Sherman to hurry forward, and writes him “…What I do expect is to get up what rations of hard bread, coffee, and salt we can and make the country furnish the balance.” Grant has still not decided which way to turn - toward Jackson or toward Vicksburg. But he is confident enough, now that he is securly on the Eastern shore, to let Pamberton make that choice. Almost the last thing Grant does before leaving Grand Gulf is to send telegram to Washington detailing his intentions and then, at 5AM the next morning, he leaves Port Gibson to rejoin his army at 14 mile Creek - before Washington can argue with his decision.
General Pemberton, meanwhile, feels he cannot afford to move against Grant. First, he is still not convinced the Union movement at Port Gibson is not an elaborate feint. And even if it is the main axis of Grant’s attack he dare not weaken the vital Haynes Bluff position to meet it. A Union coup de main on Haynes Bluff would lead to the fall of Vicksburg in a matter of hours. And Pemberton still has no reports as to the location of Sherman’s Corps. These were the very units that threatened Haynes Bluff three times before, and might be about to do so again. Pemberton’s original orders from Jefferson Davis were quite clear and have not been superseded. He must hold Vicksburg at all costs. And as he does not have enough men to firmly defend Haynes Bluff and maneuver against Grant at the same time, Pemberton feels he has no choice. He uses two divisions to improve the defenses at Vicksburg, and pushes his remaining three forward to the Big Black River crossing at Edwards, Mississippi to dig in and keep a wary eye on Grant.