Guido Carrillo scored twice as Monaco fired seven past 10-man Metz to go top of the Ligue 1 standings.
Thomas Lemar (seven), Valere Germain (23) and Bernardo Silva (39) scored in the first half to give the visitors a comfortable lead at the break.
Metz were reduced to 10 men in the 60th minute when Cheick Doukoure saw red and the floodgates then opened again, with Fabinho scoring from the penalty spot (68).
Carrillo scored a brace with his goals coming in the 72nd and 83rd minutes before Boschilia wrapped up a 7-0 victory in the final minute.