Rosecrans engaged infantry and cavalry divisions (between 4,000 and 4,500 men all told) against perhaps 3,200 Confederates.
Casualties were roughly equal, around 700, but slightly higher for the Union.
Price led the main body of his Army of the West into Iuka, Mississippi, on September 14, chasing out a small Union garrison. His mission was to prevent Maj. Gen. William S. Rosecrans's Army of the Mississippi troops from moving into middle Tennessee and reinforcing Maj. Gen. Don Carlos Buell's Army of the Ohio. If things went well, Price and his colleague Maj. Gen. Earl van Dorn would combine for an invasion of Tennessee.
Maj. Gen. Ulysses S. Grant, commanding the Army of the Tennessee, feared that Price intended to go north to join Bragg against Buell. Grant devised a plan for his left wing (8,000 men under Maj. Gen. E.O.C. Ord) to advance on Iuka from the west; Rosecrans' 9,000 soldiers were to march from the southwest, arrive at Iuka on the 18th, and make a coordinated attack the next day.
Ord arrived on time and skirmishing ensued between his reconnaissance patrol and Confederate pickets, about six miles from Iuka, before nightfall. Rosecrans informed Grant that he would not arrive at Iuka on the 18th but would begin his march at 4:30am the next morning.
On the 19th, Ord demanded Price's surrender, but Price refused. At the same time, Price received dispatches from van Dorn suggesting that their two armies join just as soon as possible at Rienzi and attack the Federals. Price told van Dorn that with Union forces bearing down on him he could not pull out of Iuka immediately. But at the same time he issued warning orders to prepare for a march the next day.
Rosecrans' army moved early on the 19th, but instead of using two roads as directed it followed the Jacinto (Bay Springs) Road, leaving the Fulton Road open. Grant had to reconsider his plans: Rosecrans would definitely be late, probably not arriving until the 19th, but what to do about his plans for an encircling attack? His solution was that Ord would wait until they heard the 'sound of the guns' and then smash into the Confederate northern flank.
When Rosecrans advanced his men fought scattered actions with Confederate troops, then, about 4pm, just after climbing a hill, the Union column halted. Not only had they been fighting and marching through the Mississippi sun, now the Confederates were in a ravine filled with timber and underbrush, excellent defensive terrain. The pause gave the Confederates a momentary edge in morale, and they struck. Even charging uphill, they overran a six-gun Ohio battery, while the Federals counterattacked from the ridge. Fighting, which Price later stated he had 'never seen surpassed,' continued until after dark; the Union troops camped for the night behind the ridge and the Confederate attack, savage as it was, had not driven them from the field.
During the day Price had pulled troops from Ord's front to fight against Rosecrans' troops. Ord did nothing, later proclaiming that he never heard any fighting and, therefore, never engaged the enemy; Grant also remarked that he had heard no sounds of battle. Price wanted to fight again on the 20th, but his subordinates convinced him to follow the original plan and join Van Dorn. At the same time, Rosecrans redeployed his men for fighting the next day rather than a pursuit.
Price's army marched out along the uncovered Fulton Road with a heavy rearguard and hooked up with Van Dorn five days later at Ripley. Although Grant's plan had Rosecrans marching along the Fulton Road and thus blocking it, Rosecrans claimed his decision avoided separating his two divisions, and Grant grudgingly approved this decision.
Rosecrans occupied Iuka and then began a pursuit but the Confederate rearguard and thick terrain meant it didn't achieve much. Price's army was ripe for the plucking, and a properly coordinated Union attack should have destroyed or captured it, but circumstances beyond anyone's control prevented a powerful attack. Price's escape is more problematic; had Rosecrans been more aggressive he probably could have cut off some part of Price's army.
Content provided by:
American Battlefield Protection Program, Heritage Preservation Services, National Park Service.