Bellamy's first-half volley put West Ham in front at Stamford Bridge
Chelsea missed the chance to go top of the Premier League as Gianfranco Zola's West Ham held on for a spirited draw.
Craig Bellamy volleyed the visitors in front, with Chelsea claiming Mark Noble had handled the ball in the build-up.
The introduction of Didier Drogba inspired Chelsea and Nicolas Anelka levelled after a neat one-touch move.
Frank Lampard wanted a penalty after he appeared to be tripped by Lucas Neill, while Carlton Cole squandered a glorious chance to win it at the death.
It was a frustrating afternoon for Luiz Felipe Scolari's Chelsea side who failed to turn their dominance into goals. But for the Hammers, the point was reward for an industrious and determined performance, typified by former Blue Scott Parker.
Before this season Chelsea had gone 86 games unbeaten at home, but the aura of invincibility that once engulfed Stamford Bridge is not as strong as it once was.
They have been defeated twice on their way to picking up just 10 points, which is in direct contrast to their travels where they have won all eight games.
After Liverpool's 2-2 draw at home to Hull on Saturday, Chelsea knew victory would send them a point clear at the top of the Premier League and they started like they meant business.
Zola, who spent seven seasons as a player at Stamford Bridge, was given a rapturous reception by the home fans but any notion of sentiment soon disappeared as the visitors were put under immediate pressure.
Michael Ballack fired a left-footed shot well over the bar before Parker denied Joe Cole, having played a one-two with Lampard.
Alex headed a good chance wide but the Hammers managed to repel the initial wave of attacks and they continued to defend manfully as Chelsea failed to seriously test Robert Green's goal.
Then, against the run of play, West Ham went in front in controversial circumstances.
Hammers were unbelievable - Zola
Chelsea were caught out by a quick throw down the left and Noble controlled the ball with his shoulder before delivering for Bellamy to finish emphatically.
The home side were furious as referee Mike Riley ignored their claims that Noble had used his arm to control the ball, with Ballack booked for his part in the protests.
Scolari reshuffled his side at half-time and threw on Drogba in place of Ballack as the hosts reverted to an attacking 4-3-3 formation.
The Ivory Coast striker was available again after suspension but had to settle for a place on the bench, however, his introduction paid immediate dividends.
He was involved in a delightful one-touch Chelsea move as he flicked the ball to Lampard who then played in Anelka to hammer home his 100th Premier League goal.
West Ham responded brilliantly and Carlton Cole had a great chance to restore his side's lead but he failed to connect properly with Bellamy's cut-back, before firing just wide.
Lampard and Drogba were both denied by Green and, on an eventful afternoon for the West Ham stopper, his uncertain attempt at punching clear was headed off the line and on to the bar by Parker.
Scolari demands more shots on goal
He soon atoned for that error, however, producing a brilliant save from Drogba's goalbound header as Chelsea hunted a winner.
They might have snatched victory in the dying minutes had Riley pointed to the spot after Lampard went down in the box under a trip from Neill.
But the best opportunity fell to former Chelsea striker Carlton Cole in injury time.
After being played clean through by Valon Behrami, he scuffed his low drive, allowing Cech to make a save low to his right and ensure Chelsea claimed a point.
Chelsea boss Luis Felipe Scolari:
"Our home is Stamford Bridge, not away, and we need to be scoring more goals here.
"We are not shooting from outside the area enough and I need to work more with the players.
"Didier Drogba is in good condition and may play more in the next game, but the other players must cooperate because when he came on we lost the midfield."
West Ham boss Gianfranco Zola:
"The performance was outstanding and the point was totally deserved.
"We are improving but we do not play with the same freedom at home as we do away from home and we will fix that."
On the upcoming January transfer window Zola added: "We will not be selling our best players, but some who are not playing in the first team may go."
Chelsea: Cech, Bosingwa, Alex, Terry, Ashley Cole, Mikel (Belletti 80), Deco, Ballack (Drogba 46), Lampard, Joe Cole (Kalou 74), Anelka.
Subs Not Used: Hilario, Ivanovic, Bridge, Ferreira.
Booked: Mikel, Ballack, Ashley Cole.
Goals: Anelka 51.
West Ham: Green, Neill, Upson, Davenport, Ilunga, Collison (Boa Morte 87), Parker, Noble (Mullins 72), Behrami, Bellamy (Di Michele 90), Cole.
Subs Not Used: Lastuvka, Faubert, Tristan, Sears.
Booked: Cole, Bellamy.
Goals: Bellamy 33.
Ref: Mike Riley (Yorkshire).
BBC Sport Player Rater man of the match: West Ham's Craig Bellamy on 7.77 (on 90 minutes).
Please note that you can still give the players marks out of 10 on BBC Sport's Player Rater after the match has finished.
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