"This was the brilliant charge of the Horse Guards that amazed the French themselves"
Napoleon at Austerlitz by Jacques François Swebach
Public DomainNapoleon at Austerlitz by Jacques François Swebach

 The Lifeguard Horse Regiment, including the Horse Guards, performed a magnificent charge at the Battle of Austerlitz, scattering the French 4th Line Infantry Regiment, under the command of Napoleon's brother, and capturing their eagle and standard. They also defeated several French infantry units. Although the Russian Guard cavalry regarded themselves as the best of the Russian army, they were newly formed and had no real battle experience before Austerlitz.

More on the cavalry at the Battle of Austerlitz.