After the Southern victory at Wilson's Creek, General Price was eager to advance to the Missouri River to regain the vital "Little Dixie" area. This area, if controlled for an extended period of time, would likely serve to add thousands of recruits to the Missouri State Guard and regalvanize pro-Southern efforts in the state. Confederate General Ben McCulloch, however, refused to cooperate and Price was forced to advance alone. After a skirmish with some Kansans at Dry Fork Creek, the MSG pressed northward. Their goal was Lexington, which was defended by the "Irish Brigade" under Col. James Mulligan. Realizing he was likely to be attacked, Mulligan built a rather formidable line of fortifications on the high ground surrounding the Masonic College north of town.
By September 18, Price had surrounded Mulligan on three sides. After capturing the riverboat landing below Lexington along with a supply boat docked there, the Missouri State Guard now had Mulligan completely invested. Meanwhile, several miles away and across the river, a Federal relief force under now Brig. Gen. Samuel Sturgis clashed with State Guard forces under Mosby Parsons. Unable to advance further, Sturgis withdrew and the siege continued.
The 20th was the day of the final showdown. Enterprising Guardsmen soaked massive hemp bales in the river and rolled them uphill towards the Federal trenches. Several lines of these "moving breastworks" worked their way inexorably towards the western end of Mulligan's defenses. With no friendly relief forces in sight and unable to counter these measures, Mulligan finally realized defeat was inevitable and surrendered at 3 o'clock. With the capture of 3,500 prisoners, 3,000 stand of arms, 10 cannon and mortars, and over $100,000 worth of commissary supplies, Price and his State Guardsmen had achieved a major victory. Unfortunately for them, the victory could not be exploited, as the thousands of new recruits gained by the victory could not be armed and a huge Federal army under General John C. Fremont would soon arrive to attack him. Price was forced to retreat back to Springfield.