Titus Labienus commanded the Optimate force and had his 8,000 Numidian cavalry and 1,600 Gallic and Germanic cavalry deploy in unusually close and dense formations for cavalry. The deployment accomplished its goal of misleading Caesar, who believed them to be close-order infantry. Caesar therefore deployed his army in a single extended line to prevent envelopment, with his small force of 150 archers up front and the 400 cavalry on the wings. In a surprising move, Labienus then extended his cavalry on both flanks to envelop Caesar, bringing up his Numidian light infantry in the center. The Numidian light infantry and cavalry began to wear the Caesarian legionaries down with javelins and arrows. This proved very effective, as the legionaries could not retaliate. The Numidians would simply withdraw to a safe distance and continue launching projectiles. The Numidian cavalry routed Caesar's cavalry and succeeded in surrounding his legions, who redeployed into a circle to face attacks from all sides. The Numidian light infantry bombarded the legionaries with missiles. Caesar's legionaries threw their pila at the enemy in return, but were ineffective. The nervous Roman soldiers bunched up together, making themselves easier targets for the Numidian missiles.

Titus Labienus rode up to the front rank of Caesar's troops, coming very near in order to taunt the enemy troops. A veteran of the Tenth Legion approached Labienus, who recognized him. The veteran threw his pilum at Labienus's horse, killing it. "That'll teach you Labienus, that a soldier of the Tenth is attacking you", the veteran growled, shaming Labienus in front of his own men. Some men however began to panic. An aquilifer attempted to flee but Caesar grabbed the man, spun him around and shouted "the enemy are over there!".

Caesar gave the order to make the battle line as long as possible and every second cohort to turn around, so the standards would be facing the Numidian cavalry in the Romans' rear and the other cohorts the Numidian light infantry to the front. The legionaries charged and threw their pila, scattering the Optimates infantry and cavalry. They pursued their enemy for a short distance, and began to march back to camp. However Marcus Petreius and Gnaeus Calpurnius Piso appeared with 1,600 Numidian cavalry and a large number of light infantry who harassed Caesar's legionaries as they retreated. Caesar redeployed his army for combat and launched a counterattack that drove the Optimates forces back over high ground. Petreius was wounded at this point. Completely exhausted, both armies withdrew back to their camps.