The Hammers eased to victory with goals either side of half-time, as Bob Bradley's Swansea side barely got out of first gear.
Andre Ayew opened the scoring with a tap-in before half-time, with Winston Reid and Michail Antonio getting second half goals to secure all three points in some style. Fernando Llorente did pull one back for the Swans, before Andy Carroll added a fourth for Slaven Bilic's men.
Swans' poor form continues
Swansea did create a couple of early chances, failing to capitalise. Alfie Mawson failed to get a header on target after an inviting ball in by Wayne Routledge, whilst Borja Baston couldn't get on the end of a ball into the box from the right.
If those chances had given the home crowd some hope, that hope was quickly dampened by West Ham's opening goal. Fabianski should have done better as Carroll headed a cross back across goal, the 'keeper failing to trap the ball as he let it run towards the back post, Ayew on hand to fire in with ease.
West Ham took that goal and used the momentum to begin dominating, allowing the likes of Dimitri Payet to unleash shots on goal, including one long range effort that was well held by Fabianski.
One good chance did come Swansea's way before half-time, Angel Rangel doing well down the right before setting up Gylfi Sigurdsson, only for the midfielder to guide his effort wide of the post.
Hammers romp to win
It didn't take long for the away side to double their lead as the game entered the second half, doing so just five minutes in. Winston Reid was the goalscorer as Swansea's set-play issues were highlighted once more, the defender beating two markers to the ball to head home.
Mark Noble almost scored the third 10 minutes later as his curling effort was blocked following good work from Payet, whilst Swansea had a penalty shout turned down when Jefferson Montero went down in the area.
That decision proved costly as West Ham did get the third goal, securign the win. Harvard Nordtveit instigated things with a shot from distance, saved by Fabianski, only for Michail Antonio to nip in and put the rebound into the back of the net.
Swansea would pull a goal back in the dying minutes, Fernando Llorente giving the home fans something to cheer. Good work from Nathan Dyer set it up, Llorente converting from inside the six-yard box.
However, their joy was short-lived once again as Carroll got a goal of his own in the battle of the big men, making it 4-1 in stoppage time. Feghouli got the assist with a nice ball to the target man, who made no mistake in volleying home.