The two armies clashed at Kalavrye on the Halmyros river. Alexios Komnenos, whose army was considerably smaller and far less experienced, tried to ambush Bryennios's army. The ambush failed, and the wings of his own army were driven back by the rebels. Alexios himself barely managed to break through with his personal retinue, but succeeded in regrouping his scattered men. At the same time, Bryennios's army fell into disorder after having seemingly won the battle, and due to the attack on its camp by its own Pecheneg allies. Reinforced by Turkish mercenaries, Alexios lured the troops of Bryennios into another ambush through a feigned retreat. The rebel army broke, and Bryennios himself was captured.