The Hammers had a brilliant opportunity when Lucas Paqueta found Vladimir Coufal inside four minutes, but Bernd Leno palmed the ball away from the right-back and Michail Antonio smashed his effort over the crossbar.
Their fast start continued without reward with Mohammed Kudus sending his attempt curling marginally over the crossbar and Paquetá firing into the side netting.
In contrast, Fulham took their first chance when Pereira coolly punished a poor touch from Konstantinos Mavropanos.
Pereira came agonisingly close to securing a second from Willian’s cross five minutes later before Mavropanos tried to atone for his error but saw a tame header routinely saved.
Joao Palhinha, James Ward-Prowse and Paqueta hit a shot from range each without causing much concern as an open first half progressed, while Pereira couldn’t capitalise on another poor Mavropanos clearance as his first-time strike was held by Lukasz Fabianski.
The goalkeeper then stopped Willian’s venomous strike and denied Rodrigo Muniz’s header from the ensuing corner, before Alex Iwobi sent his effort wide.
Ward-Prowse headed off-target from one of the first half’s last touches, and the game’s open nature continued as Muniz’s backheel was saved moments after the restart.
Leno had a scare when he spilt the ball at Danny Ings’ feet but gathered it and the Cottagers broke forward for a quick move that culminated in Iwobi’s effort being impressively tipped wide by Fabianski.
The frustrations of Mavropanos and his side grew as the centre-back was forced off injured on the hour mark and Paqueta’s header was instinctively saved by Leno shortly after.
Having previously scored once all season, Pereira applied the simplest of finishes to another blistering move for his second of the afternoon, adding some breathing space as Fulham ended their three-game winless run to go within two points of the top 10.
The Cottagers also inflicted West Ham’s second defeat in their last 12 home league matches, and there was a horrible end to the game for the Hammers as league debutant George Earthy sustained a head injury three minutes after his introduction.
Flashscore Man of the Match: Andreas Pereira (Fulham)
