An electric performance from the returning Joao Felix wasn't enough to power Chelsea to a much-needed victory at the London Stadium, as the referee and VAR denied the Blues a late penalty that would've likely delivered the win.
The visitors controlled the opening exchanges and took the lead after 15 minutes when three of their new signings combined. Mykhailo Mudryk recovered possession deep in West Ham territory before Enzo Fernandez clipped in a cross and Felix found space in the box to produce an expert side-foot volley.
The Portugal international had been frustrated by the flag minutes earlier, and Kai Havertz suffered the same fate after rounding Lukasz Fabianski.
Chelsea seemed to be in the ascendancy, but after Marc Cucurella ceded possession deep in his own half, a deep cross found former Chelsea man Emerson Palmieri at the back post, and he scuffed the ball into the net to draw West Ham level shortly before the half-hour mark.
The visitors came again, and Fabianski had to be at full stretch to keep out good efforts from both Noni Madueke and Felix before half-time.
However, Chelsea's authority waned in the second period as the hosts grew into the game. The closest they came to restoring their lead was when Michail Antonio flicked a corner inches wide of his own post.
VAR ensured there was some late drama at the end of a turgid second period. After Tomas Soucek's tap-in was ruled out for an offside in the build-up, Chelsea were denied a penalty despite Conor Gallagher's effort appearing to strike the arm of the falling Soucek on its way towards goal.
Another frustrating match for this new-look Chelsea. Here are GOAL's winners, losers and player ratings from the London Stadium!