Timo Werner and Mason Mount grabbed their second goals of the game to extend Chelsea’s lead to six.
N’Golo Kante drove through on goal and attempted to chip Fraser Forster, who could only palm the ball straight into the path of Werner who slotted it home.
Shortly after, Mount pounced in the box after a low delivery from Marcos Alonso, to extend Chelsea’s lead.
Pictures from S Sport Turkey, Bein Sports, NBC Sports, and Premier League.
Southampton fans would have expected a fight going into the second half but their defence has been non-existent. Substitutions from Ralph Hasenhuttl suggested they were going for damage limitation, with the first-half introduction of Yann Valery.