At the start of the War of the Fifth Coalition, Doumerc commanded a brigade in Nansouty's 1st Heavy Cavalry Division that included the 2nd Cuirassiers, 848 sabers, and his old 9th Cuirassiers, 875 sabers. Emperor Napoleon I of France assigned the division to an ad hoc corps led by Marshal Jean Lannes. In the Battle of Abensberg on 20 April 1809, the corps fell upon the brigades of Ludwig Thierry and Joseph, Baron von Mesko de Felsö-Kubiny near Rohr in Niederbayern. After initial resistance, the outnumbered and outgeneraled Austrians were soon fleeing down the road to Rottenburg an der Laaber with the cuirassiers slashing at the fugitives.