Takumi Minamino gave Southampton a shock lead in the 33rd minute when Nathan Redmond played an inch-perfect ball that split the defence, allowing the winger to dummy the goalkeeper before flicking a right-footed shot into an empty net.
Mason Mount would draw Chelsea level after half-time from the spot after being brought down in the box under a challenge by Danny Ings, who had no argument against the call.
Jannik Vestergaard came close to restoring Southampton’s advantage 20 minutes from full-time, but his looping header pinged off the crossbar with Edouard Mendy frozen to the spot.
Despite holding over 70 percent of the possession, Chelsea managed just three shots on target against a stingy Southampton defence.
Southampton was without first-choice right-back Kyle Walker-Peters, who limped off in the defeat to Wolverhampton last weekend with a hamstring injury, as well as Stuart Armstrong (knock).
Redmond managed to keep Hasenhuttl’s faith by starting alongside Ings for a second-straight game.
3-5-2/4-4-2): McCarthy; Bertrand, Vestergaard, Salisu, Bednarek; Minamino (Tella 76), Romeu, Ward-Prowse, Djenepo; Redmond (N’Lundulu 90+3), Ings (Adams 85)
Unused subs: Forster (GK), Stephens, Ferry, Ramsay, Jankewitz, Chauke
Goals: Minamino (33)
Bookings: McCarthy (90+2)
Chelsea (3-4-2-1): Mendy; Rudiger, Zouma, Azpilicueta; Alonso, Kovacic (Jorginho 76), Kante, James; Werner, Mount; Abraham (Hudson-Odoi 46 (Ziyech 76))
Unused subs: Arrizabalaga (GK), Giroud, Emerson, Christensen, Chilwell, Gilmour
Goals: Mount (54 PEN)
Bookings: Alonso (81)