On 29 July, Philip proclaimed the arrière-ban for northern France, ordering every able-bodied male to assemble at Rouen on the 31st. On 16 August, Edward burnt down Poissy and marched north. The French had carried out a scorched earth policy, carrying away all stores of food and so forcing the English to spread out over a wide area to forage, which greatly slowed them. The English were now trapped in an area which had been stripped of food. The French moved out of Amiens and advanced westwards, towards the English. They were now willing to give battle, knowing that they would have the advantage of being able to stand on the defensive while the English were forced to try and fight their way past them.

Edward was determined to break the French blockade of the Somme and probed at several points, vainly attacking Hangest and Pont-Remy before moving west along the river. English supplies were running out and the army was ragged, starving and beginning to suffer from a drop in morale. During the night Edward was made aware, either by an Englishman living locally or by a French captive, that just 4 miles (6 km) away, near the village of Saigneville, was a ford named Blanchetaque. Edward immediately broke camp and moved his whole force toward the ford. Once the ebbing tide had lowered the water level, a force of English longbowmen marched partway across the ford and, standing in the water, engaged a force of mercenary crossbowmen, whose shooting they were able to suppress. A French cavalry force attempted to push back the longbowmen but were in turn attacked by English men-at-arms. After a mêlée in the river, the French were pushed back, more English troops were fed into the fight, and the French broke and fled. French casualties were reported as over half of their force, while English losses were light.