Battle Of Le Cateau

Smith-Dorrien's II Corps took the brunt of a heavy assault by the German forces at Mons, with the Germans under von Kluck attempting a flanking manoeuvre. French ordered a general retreat, during which I Corps (under General Douglas Haig) and II Corps became separated. Haig's I Corps did not reach its intended position to the immediate east of Le Cateau.

http://en.wikipedia.org/wiki/Horace_Smith-Dorrien