Southampton ended Chelsea's five-match winning run to hold them to a 1-1 draw at St Mary's Stadium.
The Blues were looking to close the gap on the top three in the table -- with Southampton on a bad run of form with six straight defeats in the Premier League since the win over Liverpool -- but their task became more difficult when Takumi Minamino's composed finish put the home side ahead against the run of play.
Mason Mount coolly levelled from the penalty spot after he was tripped by Danny Ings before Jannick Vestergaard hit the woodwork with goalkeeper Edouard Mendy beaten all ends up.