The catastrophe was already in motion before Korsun. On 16 May 1648, Khmelnytsky's forces had destroyed a Polish vanguard at Zhovti Vody, and thousands of registered Cossacks who had marched for the Crown switched sides. The Grand Crown Hetman Mikolaj Potocki, whose own son had commanded the lost vanguard, learned the full scale of the defeat only when a lone survivor reached him near Cherkasy. He had come north as far as Korsun with the Field Crown Hetman Marcin Kalinowski and their combined army, and there he halted, hoping to wait for Prince Jeremi Wisniowiecki's reinforcements. But Khmelnytsky's advance parties were already crossing the Tiasmyn and then the Ros. Potocki ordered the town of Korsun burned and readied his camp for a fight he was increasingly unlikely to win.

Facing a larger enemy and cut off from relief, Potocki did the sensible thing and decided to retreat, forming his men and wagons into a defensive column, the tabor, for the march to Bohuslav. But Khmelnytsky had read the move. He sent his fierce colonel Maksym Kryvonis, nicknamed Crooked-Nose, ahead to a swampy valley between two steep slopes at Horokhova Dibrova, about a mile and a half from Korsun. Through the night, Kryvonis's men dug trenches, felled trees, and barricaded the road, turning the ravine into a sealed corridor. Meanwhile other Cossacks dammed the river at Stebliv to flood the ground and slow the Polish escape. The trap was ready before the Commonwealth army had even begun to move.

At dawn the retreat began, and the Cossacks and Tatars let it come, shadowing the column but holding back until the Poles were deep inside the valley at noon. Then the ground itself closed on them. Wagons jammed against the barricades, cavalry could not maneuver on the boggy floor, and from both wooded slopes the Cossacks poured down fire and steel. Whole divisions were cut apart in the chaos. Only about fifteen hundred men, under a Colonel Korycki, fought clear and escaped. Both Hetmans, Potocki and Kalinowski, were taken prisoner, later handed to the Tatars. Over eight thousand troops and more than forty cannon were captured, and the rest of the army was killed or seized. It was less a battle than a demolition.

In two swift blows, Zhovti Vody and Korsun, Khmelnytsky had annihilated the field forces of one of Europe's great powers and captured both its senior commanders. The Commonwealth was left, for a stunned moment, without an army in the field and without a Hetman to lead one. Khmelnytsky did not pause. He gathered his growing host and turned toward Bila Tserkva, carrying the uprising deeper into the heart of the country and setting in motion the long war that would give rise to the Cossack Hetmanate. The wooded ravine near Korsun looks unremarkable now, folded into the same gentle Cherkasy landscape that would see another army trapped nearby three centuries later. But it was here that a rebellion became a revolution.