A defeat at the Battle of Pilot Knob in late September and the strength of Union positions at Jefferson City led Price to abandon the main objectives of the campaign; instead he moved his force west towards Kansas City, where it was badly defeated at the Battle of Westport by Major General Samuel R. Curtis on October 23.

With his men low on ammunition, Blunt was considering a retreat shortly before sundown when reinforcements arrived in the form of Brigadier General John B. Sanborn and his brigade.

[7] Originally, Price and his army had hoped to capture St. Louis, but a defeat at the Battle of Pilot Knob in late September dissuaded the Confederates from assaulting that city.

Major General William S. Rosecrans, commander of the Union Department of the Missouri, began mobilizing troops against Price.

On October 23, Union Major General Samuel R. Curtis and the Army of the Border caught up with Price near Kansas City and badly defeated him in the Battle of Westport.

The Army of Missouri then began retreating through Kansas, and was defeated three times on October 25, including the Battle of Mine Creek, which was a disastrous rout in which large quantities of supplies and soldiers were captured.

Union troops reported finding Confederate stragglers dying of starvation during the retreat, and Price lost many men to desertion.

[17] The Confederates were harvesting corn when the Union troops arrived and their skirmishers were quickly driven away from their position west of the town near the Mathew H. Ritchey Farm.

[24][25] Shelby deployed his men 500 yards (460 m) away on the other side of the farm, with the brigades of Thompson and Colonel Sidney D. Jackman in the center and two small mounted detachments covering the flanks.

[28] The two sides' artillery opened fire, Collins's Battery having the early advantage over McLain, whose pieces had trouble finding the range of the Confederates.

[19][30] Either two[29] or four[31] mountain howitzers were added to the Union line by Hoyt; they were more effective than McLain's pieces, but could not gain an advantage over Collins.

[35] Blunt, concerned that his men would run out of ammunition, began making preparations to withdraw from the field and positioned McLain's Battery on an elevation behind his main line.

[33] By now, it was approaching sundown, and Union reinforcements commanded by Brigadier General John B. Sanborn arrived on the field at around 17:00, having made a forced march from Fort Scott, Kansas after receiving orders from Curtis to join Blunt earlier in the day.

[35] With the Union having thrown fresh troops into the fray and with the artillery advantage growing more marked, Shelby ordered a withdrawal.

[40] Elements of Fagan's command arrived to reinforce Shelby during the retreat, but the Confederates still withdrew to some woods near their original camp.

Curtis reported that the Confederates had been "conquered", while Price claimed that Blunt had been driven back 3 miles (5 km) and to have inflicted severe casualties.

[38] Shelby's chief of staff, John Newman Edwards, stated that "another beautiful victory had crowned the Confederate arms".

[41] Both the American Battlefield Trust and the Civil War Sites Advisory Commission interpret the outcome as a Union victory.

[42] It is known that 46 wounded Confederates were captured by Union troops when they were abandoned after the battle due to Price's army's inability to transport them.

[45] During the night after the battle, most of Shelby's men left the field to rejoin Price's main command, having completed their mission of providing a rear guard.

[46] Sanborn's men spent the night east of Newtonia, while the other two Union brigades fell back to the northwest of the town.

[40] Price's army, which Castel described as being essentially an armed mob after the October 25 Battle of Marmiton River, began falling completely apart.

[18][47] Rosecrans had received orders from General Ulysses S. Grant to divert any troops not needed to deal with Price east of the Mississippi, so two brigades, including Sanborn's, were detached from Curtis on October 29.

[53] The Ritchey House and 25 acres of the battlefields including the Old Newtonia Cemetery were added to Wilson's Creek National Battlefield in 2022 by the Consolidated Appropriations Act, 2023, despite National Park Service opposition due to the lack of connection, need for protection, or enhancement of public enjoyment.