Derby's force embarked at Southampton at the end of May 1345. Bad weather forced his fleet of 151 ships to shelter in Falmouth for several weeks en route, finally departing on 23 July. The Gascons, primed by Stafford to expect Derby's arrival in late May and sensing the French weakness, took the field without him. The Gascons captured the large, weakly garrisoned castles of Montravel and Monbreton on the Dordogne in early June; both were taken by surprise and their seizure broke the tenuous Truce of Malestroit. Stafford carried out a short march north to besiege Blaye. He left the Gascons to prosecute this and proceeded to Langon, south of Bordeaux, to set up a second siege. The French issued an urgent call to arms.

Meanwhile, small independent parties of Gascons raided across the region. Local French groups joined them, and several minor nobles threw in their lot with the Anglo-Gascons. They had some successes, but their main effect was to tie down most of the French garrisons in the region and to cause them to call for reinforcements – to no avail. The few French troops not garrisoning fortifications immobilised themselves with sieges of English-controlled fortifications: Casseneuil in the Agenais; Monchamp near Condom; and Montcuq, a strong but strategically insignificant castle south of Bergerac. Large areas were left effectively undefended.

On 9 August Derby arrived in Bordeaux with 500 men-at-arms, 1,500 English and Welsh archers, 500 of them mounted on ponies to increase their mobility,and ancillary and support troops, such as a team of 24 miners. The majority were veterans of earlier campaigns. After two weeks of further recruiting and consolidation of his forces Derby decided on a change of strategy. Rather than continue a war of sieges he determined to strike directly at the French before they could concentrate their forces. The French in the region were under the command of Bertrand de l'Isle-Jourdain, who was assembling his forces at the communications centre and strategically important town of Bergerac. This was 60 miles (97 kilometres) east of Bordeaux and controlled an important bridge over the Dordogne River.