As soon as Wellington perceived the mistake, he saw that his opportunity had come. Orders were despatched in all directions and, suddenly, the two divisions, hidden from the sight of the French behind the Hermanito, dashed down into the valley; where two other divisions joined them. The 4th and 5th were in front, with Bradford's Portuguese; and the 6th and 7th formed the second line; while the Spanish troops marched between them and the 3rd division, forming the extreme right at Aldea Tejarda. The light divisions of Pack's Portuguese and the heavy cavalry remained in reserve, on high ground behind them. In spite of a storm of bullets from Maucune's guns, the leading divisions marched steadily forward and, while the third division dashed across the valley and, climbing the ridge, barred his progress, the main line advanced to attack his flank.

Marmont, seeing the terrible danger in which Maucune was involved, sent officer after officer to hasten up the troops from the forest and, with his centre, prepared to attack the English Hermanito, and to drive them from that portion of the village they still held; but as he was hurrying to join Maucune a shell exploded near him, hurling him to the ground with a broken arm, and two deep wounds in his side. This misfortune was fatal to the French chances. Confusion ensued, and the movements of the troops were paralyzed.

It was about five o'clock when the 3rd division, under Pakenham, fell upon Maucune's leading division; and two batteries of artillery suddenly opened fire, on their flank, from the opposite height. Having no expectation of such a stroke; and believing that the British were, ere this, in full retreat along the Ciudad road, the French were hurrying forward, lengthening out into a long, straggling line.

The onslaught of Pakenham's division was irresistible, supported as it was by guns and cavalry. Nevertheless, the French bore themselves gallantly, forming line as they marched forward, while their guns poured showers of grape into the approaching infantry. Nothing, however, could stop them. Pressing forward, they broke the half-formed lines into fragments, and drove them back in confusion upon the columns behind. The French cavalry endeavoured to check the British advance, by a charge on their flank; but were repulsed by the infantry, and the British light horsemen charged, and drove them off the field.

Pushing forward, Pakenham came upon the second half of the division they had defeated, formed up on the wooded heights; one face being opposed to him, and the other to the 5th division, Bradford's Portuguese, and a mass of cavalry moving across the basin. The French had been already driven out of Arapiles, and were engaged in action with the 4th division; but the battle was to some extent retrieved, for Clausel's division had arrived from the forest and reinforced Maucune; and spread across the basin, joining hands with the divisions massed near the French Hermanito.

Marmont had been carried off the field. Bonnet, who had succeeded him, was disabled; and the chief command devolved on Clausel, a general of talent, possessing great coolness and presence of mind. His dispositions were excellent, but his troops were broken up into lines, columns, and squares. A strong wind raised the sandy soil in clouds of dust, the sinking sun shone full in the faces of his troops and, at once, concealed the movements of their enemies from them, and prevented them from acting with any unity.

Suddenly, two heavy bodies of light and heavy cavalry broke from the cloud of dust and fell upon them. Twelve hundred Frenchmen were trampled down and, as the cavalry rode on, the third division ran forward, at the double, through the gap that they had formed. Line after line of the French infantry was broken and scattered, and five of their guns captured by one of the squadrons. Two thousand prisoners were taken, and the three divisions that Maucune had commanded were a mass of fugitives.

In the meantime, a terrible battle was raging in the centre. Here Clausel had gathered three fresh divisions and, behind these, the fugitives from the left rallied. He placed three others, supported by the whole of the cavalry, to cover the retreat; while yet another remained behind the French Hermanito. Pack's Portuguese were advancing against it, and arrived nearly at the summit, when the French reserves leapt from the rocks and opened a tremendous fire on their front and left flank; and the Portuguese were driven down the hill, with much loss. Almost at the same moment, one of the regiments of the 4th division were suddenly charged by 1200 French soldiers, hidden behind a declivity, and driven back with heavy loss.

For a moment, it seemed that the fate of the battle might yet be changed; but Wellington had the strongest reserve, the sixth division was brought up and, though the French fought obstinately, Clausel was obliged to abandon the Hermanito; and the army began to fall back, the movement being covered by their guns and the gallant charges of their cavalry.

The whole of the British reserves were now brought into action, and hotly pressed them; but, for the most part maintaining their order, the French fell back into the woods and, favoured by the darkness, and nobly covered by Maucune, who had been strongly reinforced, they drew off with comparatively little loss, thanks to the Spaniards' abandonment of the fort guarding the ford at Alba.