And it was so on the morrow, that Saul put the people in three companies; and they came into the midst of the host in the morning watch, and slew the Ammonites until the heat of the day: and it came to pass, that they which remained were scattered, so that two of them were not left together. Put the people in three companies - Intending to attack the Ammonites in three different points, and to give his own men more room to act.
In the morning watch - He probably began his march in the evening, passed Jordan in the night, and reached the camp of the Ammonites by daybreak.
That two of them were not left together - This proves that the rout was complete.