When the Civil War broke out, Sayers joined the Confederate States Army's 5th Texas Regiment, a cavalry unit led by General Tom Green. He participated in the Battle of Valverde in New Mexico in February 1862, and was recommended for promotion for his bravery in capturing an artillery battery. Later that year he returned to Texas with his regiment before being sent to Louisiana, where he was wounded in the Battle of Fort Bisland in April 1863. His actions during that conflict led to his promotion to major, and he became Green's chief–of–staff. Sayers was wounded again in April 1864 at the Battle of Mansfield. After Green died at the Battle of Blair's Landing, Sayers became the assistant adjutant to General Richard Taylor.