Diafra Sakho broke Swansea City hearts with a late winner to hand West Ham a perhaps unwarranted 1-0 victory.
Paul Clement's charges had seemed on course to prevent the home side from scoring for the first time in 32 encounters but the Senegal striker's 90th-minute strike ensured all three points stayed in west London.
The defeat for the Swans means the south Welsh club conceded for the first time on the road this term and still only boast one Premier League victory in 2017/18.
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Michail Antonio, a surprise inclusion after he trudged off last Saturday with a groin strain, drew a fine stop from Lukasz Fabianski with a bouncing volley from Aaron Cresswell's teasing centre.