Although West Ham totally dominated a one-sided second half, they could not recover the self-inflicted damage of the first, which left our London rivals in an unassailable 2-0 lead.
There were only four minutes of this derby played when a long throw from Luke Young on the right fell kindly to Claus Jensen, who lashed his right-foot shot into the roof of the net from 10 yards.
Hammers' back four struggled against strikers Jason Euell and Mathias Svensson all half and it was no surprise when another corner from the left caused panic. Svensson completely lost Michael Carrick and when his free header was cleared only as far as the penalty spot, Jon Fortune drove the ball through the pack and into the bottom far corner.
Eight goals conceded in three games, Glenn Roeder will doubtless be anxious to solve his side's defensive weaknesses before West Brom - who climbed above us with their first win today - visit Upton Park in 10 days.
One option will be a recall for Ian Pearce or a first start for new signing Gary Breen. Neither defender left the subs' bench today as the boss kept faith with Tomas Repka and Christian Dailly, but both endured a difficult afternoon.
Despite rare forays into Hammers' half in the second half, long throws and corner continued to haunt Hammers and Euell was only inches wide from scoring with his head 12 minutes from time.
By then West Ham were resigned to a defeat much of their own making. Joe Cole maintained his superb start to the season with another outstanding performance that should further press his claims for a start for England against Portugal next Saturday, but even the midfield marvel could not conjure a goal.
Cole, who gave England team-mate Chris Powell such a torrid time on the right flank, twice went close to opening the scoring in the first 17 minutes. While central midfield pair Carrick and Eduoard Cisse seemed reluctant to get forward in support of Fredi Kanoute and Jermain Defoe, it was the elusive Cole who was everywhere, probing for the opening that wouldn't come.
When Hammers did hit the target, Charlton keeper Dean Kiely was unbeatable, turning a sharp Defoe shot from 20 yards around his right-hand upright.
Roeder sent Pearce, Breen and Steve Lomas - recovered from a shin injury - back onto the pitch for a half-time kickabout, which indicated a shake-up. But the same 11 re-emerged from the tunnel for the second half and, whatever the manager said, the home side did at least raise the tempo.
Cole almost scored the goal his performance deserved in the 53rd minute, when he dummied his marker, turned and cracked a left-foot shot from 25 yards that just cleared the crossbar at the Bobby Moore Stand end.
The 32,424 crowd welcomed the return of Lomas in the 62nd minute, but booed the departure of Cisse, whom they felt had done well enough. The switch made sense, though, because the tall Frenchman was visibly wilting in the East London sunshine and the Irishman brought a new sense of urgency to proceedings.
Sinclair chipped a deft pass to the overlapping Nigel Winterburn - playing on despite a broken nose sustained in a 21st minute clash with Mathias Svensson - and only Kiely's fingertips prevented the veteran's first goal at Upton Park, while Richard Rufus underlined the Addicks' quality defending throughout the second half when he just cleared a Kanoute cross that both Sinclair and Defoe were ready to convert at the near post.
Cole and Sinclair switched flanks in an effort to pose new problems to the men in black in the latter stages. Cole delivered another excellent cross but Kanoute's acrobatic shot dropped wide of the post, as did his header from another Cole cross.
West Ham never stopped pressing, with Sinclair heading another Kanoute cross over, but nothing went their way up front today. Substitute Titi Camara came off the bench with 14 minutes remaining and showed some useful touches, but failed to add the spark of inspiration needed to turn the tide.
With only Bolton (who play tomorrow) separating Hammers from bottom spot, the fans were understandably frustrated that this defeat should follow on the back of that epic performance against Arsenal. They will expect nothing less than three points against West Brom here next time out.
Paolo Di Canio should be fit in time for the visit of newly-promoted Albion. His delivery from corners and free-kicks will be much needed on this evidence, but the Italian maestro cannot be expected to solve defensive worries, too..
Minute-by-minute:
2 - Hammers are handed an excellent opportunity to open the scoring, as Rufus is penalised for a foul on Cole on the edge of the area. However, an unusual free-kick routine involving Defoe, Sinclair and Carrick comes to nothing as the Charlton defence read their plan.
4 - GOAL. Upton Park is left stunned as Charlton take a surprise lead. Young's long throw from the right isn't dealt with by the Hammers defence and a grounded Rufus touches the ball to Jensen, who smashes his shot into the roof of the net from eight yards out. West Ham United 0 Charlton Athletic 1.
9 - Hammers fight back and Cisse is unlucky with a surging run and low shot from the edge of the area that Kiely holds well.
14 - The hosts are beginning to settle into their more familiar style of attacking football and Cole goes close with a bending low shot after playing a clever one-two with Cisse.
17 - Cole is now finding his range and tests Kiely again with a dangerous left-foot effort that hits the side-netting.
20 - After Schemmel's corner is only half-cleared, Dailly's chip into the six-yard box falls for Repka, who unfortunately misses his kick with the goal at his mercy, and Charlton clear their lines.
21 - Winterburn ends up with a bloody nose after an accidental clash with Svensson as the pair chase a long ball down the touchline.
26 - James rushes out from his goal to punch another long throw from Young, but the ball falls at the feet of Bart-Williams, whose goalbound effort from the edge of the area is only kept out by the quick-thinking of Winterburn, who heads clear after covering James on the goal-line.
30 - Sinclair's cross from the left appears to be handled by Fortune, who lives up to his surname as referee Winter waves play on.
36 - Carrick BOOKED for a foul on Jensen.
40 - Defoe is denied an equaliser by a tremendous save from Kiely, who dives low to his right to somehow palm the striker's fierce low effort up and over the bar.
44 - GOAL. Disaster strikes as Charlton grab a second just moments before the break. A deep corner from Jensen is met by an unmarked Svensson, who heads the ball goalwards. A feeble attempt to clear the danger sets up Fortune, who sweeps the ball past a crowd of bodies into the net. West Ham United 0 Charlton Athletic 2.
Added time: 2 minutes.
Half-time: West Ham United 0 Charlton Athletic 2.
Second Half:
51 - Sinclair cuts in from the left and fires a low shot that flies just wide of the near post.
53 - Cole, doing his best to spark off a comeback, sees a blistering left-foot shot from the edge of the area fly just inches over the bar.
59 - Cole BOOKED for dissent.
62 - Substitution for West Ham, Lomas replaces Cisse.
68 - Repka BOOKED for unsporting behaviour.
70 - Rufus BOOKED for a foul on Sinclair.
73 - Charlton almost grab a third from the unlikely source of Rufus, who receives a return pass inside the area and is only denied a goal by a saving tackle from Repka. The ball rebounds to Euell six yards out, but Carrick clears the danger.
74 - Sinclair's lofted pass reaches Winterburn in the six yard box, but the veteran defender sees his toe poke turned round the post by Kiely.
75 - Euell collects Svensson's flick-on from a Kiely clearance and fires in a shot that is deflected just wide off the boot of Dailly.
76 - Substitution for West Ham, Camara replaces Winterburn.
79 - Substitution for Charlton, Bartlett replaces Svensson.
Added time: 3 minutes.
Full-time: West Ham United 0 Charlton Athletic 2.