Kelley Blanchflower made it five goals in five games for the Hammers Ladies but could not stop them losing 3-2 at Brighton & Hove Albion.
The in-form forward had pegged back the hosts on Sunday after they struck first. It meant the teams went in level at half-time and the Hammers were able to strike first after the break when Becky Merritt headed in Jess Barling's cross.
However, the home side were back in it on 70 minutes with a 25-yard free-kick that gave Nikki Duncan no chance in goal. Both teams then pushed for a winner, which went to Brighton when they pounced from close range with just four minutes to play.
The Hammers will hope for better luck when they hit the south coast again next Sunday against Portsmouth.