In need of a positive result having tasted victory just once in seven PL fixtures (D3, L3), Chelsea were on the front foot for much of the first period, but the Blues often lacked intensity in their build-up play.
There were certainly flashes of intent, with Noni Madueke heavily involved, curling narrowly wide of the far post 15 minutes in, then teeing up Enzo Fernandez for a shot that was dragged into a similar area shortly after the half-hour mark.
Late in the half, Madueke laid off Jadon Sancho, who cut inside and sent a swerving shot off-target.
For all their dominance, the hosts were lacking cutting edge, and that was punished moments later when Levi Colwill’s loose pass was intercepted by the returning Jarrod Bowen, who confidently slotted a low strike into the bottom corner.
On the stroke of half-time, Alphonse Areola had to produce an excellent fingertip save to keep out Cole Palmer’s free-kick, ensuring the Hammers went into the break with their noses in front.
Far from reinvigorated after the restart, Chelsea were in desperate need of fresh impetus as West Ham exerted some pressure.
It took just seven second-half minutes for Enzo Maresca to turn to his bench, and with 61 minutes on the clock, the home boss had made four alterations as he searched for a response.
Those changes had an instant impact, as substitute Pedro Neto struck for the first time since November, starting a dangerous series of events with a whipped cross that eventually made its way back to him via a deflection for a simple finish.
That goal seemed to spark the contest into life, with Mohammed Kudus heading Bowen’s first-time cross onto the post, albeit from an offside position.
However, at the other end, a much-improved Chelsea performance eventually yielded another goal as the Blues took the lead thanks to Aaron Wan-Bissaka, whose unfortunate intervention resulted in Palmer’s cross looping over Areola.
Further chances came Cheslsea’s way in the final minutes, as Areola prevented another OG when Konstantinos Mavropanos headed towards his own net, shortly before Palmer bent an effort just wide.
Those missed opportunities ultimately proved immaterial as Tosin Adarabioyo blocked a late Kudus attempt, helping see out three points that takes the Blues back into the top-four, having lost just once in 17 home matches in all competitions (W12, D4).
Meanwhile, a third consecutive PL H2H defeat for the first time since 2011 leaves the Hammers 15th, seven points adrift of the top half.