Southampton snatched a late point at the London Stadium through Chelsea loanee Lesley Ugochukwu, denying the hosts a first Premier League win since February.
Jarrod Bowen's goal just after the break looked to have set the Hammers on the way to three points, but the Saints drew level in added time.
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Jarrod Bowen opened the scoring just after the break but the Hammers couldn't hold on
Chelsea loanee Lesley Ugochukwu snatched a point for Simon Rusk's side in extra time
Match Facts
West Ham (4-2-3-1): Areola; Coufal, Todibo, Kilman, Emerson (Scarles 80'); Soler, Ward-Prowse (Mavropanos 86'); Bowen (Ferguson 86'), Kudus (Guilherme 75'), Paqueta; Fullkrug (Soucek 80')
Subs: Fabianski, Cresswell, Irving, Rodriguez
Goal: Bowen 47'
Booked: Coufal, Kilman
Manager: Graham Potter
Southampton (3-4-2-1): Ramsdale; Harwood-Bellis (Stewart 85'), Bednarek, Stephens; Walker-Peters, Downes, Ugochukwu, Manning (Welington 85'); Fernandes, Sulemana (Dibling 74'); Onuachu (Archer 69')
Subs: McCarthy, Aribo, Bree, Smallbone, Wood-Gordon
Goal: Ugochukwu 90+3'
Booked: Onuachu
Manager: Simon Rusk
Ref: Andrew Kitchen