When war with France broke out in 1809, von Hiller was given command of VI Armee Korps covering the left wing of the main Austrian army. When Emperor Napoleon I of France fell on the Austrian left wing on 20 April at the Battle of Abensberg, Hiller arrived and took command of the V, VI, and II Reserve Armeekorps. Defeated at Abensberg and on 21 April at the Battle of Landshut, he became separated from the main army. On 22 April Archduke Charles was beaten at the Battle of Eckmühl and retreated to the north bank of the Danube. Not realizing he was alone on the south bank, Hiller attacked Marshal of France Jean-Baptiste Bessières and won a minor victory in the Battle of Neumarkt-Sankt Veit on 24 April. Finally realizing the odds against him, he retreated in good order toward Linz from 25 April to 3 May. On the latter date he fought a savage action with André Masséna's corps at the Battle of Ebelsberg. This defeat forced von Hiller to withdraw across the Danube at Mautern.