Liga champions Atletico Madrid thrashed league leaders and city rivals Real Madrid 4-0 in Los Blancos' heaviest defeat since losing 5-0 to Barcelona in 2010.
Tiago and Saul Niguez gave the hosts a 2-0 half-time advantage at the Vicente Calderon in a five-minute spell.
Niguez's goal was particularly impressive as he put away a spectacular bicycle kick.
Atletico danger men Antoine Griezmann and Mario Mandzukic turned the big result into a massive hammering in the second period.
Though Real still lead the table with 54 points, Atletico are now third with 50 - the same as second-placed Barcelona, who can go one point behind Real if they defeat Athletic Bilbao on Sunday.