Gianfranco Zola made an unhappy start to his reign as West Ham manager as Chris Brunt struck a late winner for West Brom at The Hawthorns.
Zola had seen his new side recover from conceding an early goal to James Morrison to lead 2-1 thanks to goals from Mark Noble and captain Lucas Neill.
But a penalty from Roman Bednar leveled matter for the home side before Brunt grabbed the clincher seven minutes from time to give Albion their first win of the Premier League campaign.
Zola watched from the stands and will be aware that much work needs to be done defensively if the Hammers are to make strides forward.
Tony Mowbray's side just about deserved their victory with home captain Jonathan Greening a key figure in midfield. Carlton Cole battled hard up front for the visitors but lacked support.
Morrison put the Baggies ahead after only two minutes, however there appeared little danger when a left-footed cross from Brunt went across the Hammers box.
Borja Valero was first to react to the loose ball though and he had time to pick out the run of Morrison who sent a glancing header wide of Robert Green into the corner of the net, for Albion's first goal in open play since returning to the top flight.
West Ham found plenty of space to exploit down the left flank, and West Brom goalkeeper Scott Carson parried away a curling effort from Dean Ashton who shortly afterward was substituted due to a shoulder problem.
Both defenses looked suspect and Green completely missed a corner from Greening, only for Bednar to head wide from close range.
Robert Koren had a golden chance to double the home side's lead when he found himself with only Green to beat but the goalkeeper was able to block his shot.
The visitors started to enjoy more of the possession and drew level after 28 minutes.
Calum Davenport's cross found Valon Behrami whose downward header was parried by Carson straight to Noble and he made no mistake from close range.
A clearance from Leon Barnett then rebounded off Behrami straight to substitute David Di Michele who forced a save out of Carson at the expense of a corner - and from it West Ham went ahead.
Noble's center was headed back across goal by Davenport and Neill volleyed home from close range.
But within 60 seconds West Brom were level.
Green brought down Barnett and up stepped Bednar to drill the penalty powerfully into the net.
It was his second successful spot-kick of the campaign, after putting one away against Everton in the previous home game.
Albion knocked the ball around in confident fashion at the start of the second half and a fine move ended with Paul Robinson finding Bednar in space inside the West Ham box, but Green reacted quickly to parry the shot from the former Hearts player.
Bednar then created half a yard of space for himself after turning past Davenport but the defender recovered to block the eventual shot.
Home boss Tony Mowbray made a double change after 64 minutes with Luke Moore and Do-Heon Kim replacing Valero and Morrison respectively.
Within 60 seconds West Ham had brought on Julien Faubert for Behrami.
Kim quickly went into referee Lee Probert's book, receiving a yellow card for a challenge on Noble.
In the 83rd minute Brunt put Albion ahead after racing onto a pass from Robinson and it proved to be worth three points.
Scott Parker should have equalized in injury time but was denied by Carson.
