A little after 13:00, I Corps' attack began in large columns. Bernard Cornwell writes "[column] suggests an elongated formation with its narrow end aimed like a spear at the enemy line, while in truth it was much more like a brick advancing sideways and d'Erlon's assault was made up of four such bricks, each one a division of French infantry". Each division, with one exception, was drawn up in huge masses, consisting of the eight or nine battalions of which they were formed, deployed, and placed in a column one behind the other, with only five paces interval between the battalions.

The divisions were to advance in echelon from the left at a distance of 400 paces apart—the 2nd Division (Donzelot's) on the right of Bourgeois' brigade, the 3rd Division (Marcognet's) next, and the 4th Division (Durutte's) on the right. They were led by Ney to the assault, each column having a front of about a hundred and sixty to two hundred files.

The leftmost division advanced on the walled farmhouse compound La Haye Sainte. The farmhouse was defended by the King's German Legion. While one French battalion engaged the defenders from the front, the following battalions fanned out to either side and, with the support of several squadrons of cuirassiers, succeeded in isolating the farmhouse. The King's German Legion resolutely defended the farmhouse. Each time the French tried to scale the walls the outnumbered Germans somehow held them off. The Prince of Orange saw that La Haye Sainte had been cut off and tried to reinforce it by sending forward the Hanoverian Lüneburg Battalion in line. Cuirassiers concealed in a fold in the ground caught and destroyed it in minutes and then rode on past La Haye Sainte, almost to the crest of the ridge, where they covered d'Erlon's left flank as his attack developed.