Chelsea dominated from start to finish, Maren Mjelde scoring the first goal in the seventh minute, slotting into the bottom left of the goal after West Ham failed to clear an Erin Cuthbert corner.
The second came in the 12th minute when Bethany England got on the end of a perfectly-timed ball from Cuthbert, and went beyond West Ham goalkeeper Courtney Brosnan for a calm finish.
Sophie Ingle then made it 3-0 in the 44th minute as she managed to get her head on the ball in the middle of a goalmouth scramble following a corner.
The thrashing continued from the start of the second half, Cuthbert making it 4-0 in the 52nd minute. She was lucky to be onside as she received the ball on the run, taking it past defender Grace Fisk and firing it in from outside the box.
West Ham manager Matt Beard’s protests about the lack of offside ruling against Cuthbert earned him a yellow card.
Chelsea’s fifth goal came as England scored her second of the game in the 56th minute with a headed goal from a corner.
In the 61st minute Mjelde stormed into the six-yard box to fire a cross into the back of the net just as Brosnan thought it was coming safely into her hands, making it 6-0.
Next it was substitute Ramona Bachmann putting the ball in the back of the net after West Ham failed to clear a Jess Carter cross in the 87th minute. Finally, Chelsea’s eighth goal came again from a substitute as Emily Murphy headed home in the 90th minute.