Southampton came from behind to earn their second win of the fledgling Premier League season and move above a Chelsea side lacking cohesion and a cutting edge at St Mary’s.
Raheem Sterling is the Blues’ top scorer and got Thomas Tuchel’s side off to a promising start with his third goal in two games thanks to a calm swivel and finish in the 23rd minute.
But another former Manchester City player levelled moments later, with Romeo Lavia firing a superb effort beyond Edouard Mendy after Chelsea failed to properly clear a corner.
From then on Southampton were the better side and scored what proved to be the winner before the break, when Romain Perraud picked out Adam Armstrong and his effort deflected off Kalidou Koulibaly and into the net.
Ralph Hasenhuttl’s outfit climb to seventh as a result of the deserved victory, level on seven points with Chelsea but above them on goals scored.