The king himself, it is said, had two horses killed under him, and apparently "was much beaten by swords and maces". Under cover of his men, he retreated to the walled priory within the town.
The army under de Montfort then entered the town and took part in hand-to-hand fighting which probably lasted until mid-morning.
Upon returning to Lewes, Edward found his father's army scattered. His first reaction was to strike at de Montfort's baggage train which was placed up on the Downs. One wagon, flying the de Montfort banner of a silver twin tailed lion rampant on a red field, was set upon and several royalist citizens who happened to be there were killed in the fury of what Edward had hoped was an attack on Simon himself, as the Earl had recently (through his leg injury which had occurred the previous December) had to rely on transportation of this kind.
Following this action Edward rallied his men and approached Lewes. The de Montfortians came out to meet him, and battle was joined. Warenne, William de Valence, Guy de Lusignan and Hugh Bigod fled. Weakened, Edward, with the remainder of his force, circled the town towards the castle but then managed to find and join the king in the priory.
With the king and Edward in the priory were Richard's son Henry, along with "many knights" including Roger Mortimer and other notable Marcher lords. 500 metres away the castle also lay in royalist hands, where John Giffard was held a valuable prisoner.
De Montfort's forces continued to attack the castle during the day and a great part of the town was set on fire with burning arrows. The garrison put up a strong defence, however, and the rebels began to besiege the priory, where the church was also set alight with arrows - although these flames were quickly doused.