The Hammers made it seven games unbeaten as they caused a Chelsea meltdown by inflicting a fifth defeat from 10 games on Jose Mourinho's side.
But what did we learn about West Ham from the game?
1) West Ham are serious top six contenders
Ahead of the East vs West London derby, pundits such as Jamie Carragher in The Mail said the visit of the Blues to Upton Park would prove whether Bilic's side has what it takes to compete with the top six. The Hammers boast the best away record in the Premier League after wins over Arsenal, Liverpool, Manchester City and Crystal Palace but have been indifferent at home. But in beating the Blues the Irons have, according to experts like Carragher, announced themselves as genuine challengers for a top six spot. Bilic's side boast 20 points from 10 games. That's an average of two points per game which isn't just Champions League form, it's title winning form.
2) There's more to Slaven Bilic than beards and beanie hats, he is an astute tactician
Slaven Bilic is well respected for his work as Croatia manager. But he also has a reputation for being a cool, earring and beanie hat wearing, beard sporting, cigarette smoking rock band guitarist manager who entertains as much on the touchline as his team does on the pitch. Well he is all of those things, but what he has proved this season is that he has the tactical acumen to thrive in the Premier League. The way he has set his team up away from home has been nothing short of perfect. He has embraced the West Ham way and attacks teams with intent while not compromising the defensive side. He has already taken on and beaten some of the top managers in the league with the scalps of Arsene Wenger, Manuel Pellegrini, Alan Pardew and Jose Mourinho to his name. He can also adapt during the match as he showed against Chelsea where he realised the Blues were getting themselves on top in the second half and he brought on Andy Carroll and Pedro Obiang and asked different questions of Mourinho's side, which ultimately won them the game.
3) Andy Carroll is back
It's official Andy Carroll, the Premier League's biggest sicknote, is back in business. After eight months out the big striker has been slowly eased back into action in the last month and got his first goal since January to seal all three points for the Hammers. Carroll has made just 57 appearances in more than three years at the club. But he looks fitter, leaner and more focused than ever. He also showed with a few of his touches that he can fit in with Bilic's attacking football on the floor and is not just a head to aim at as was the case under Sam Allardyce. The question for Carroll now is can he stay fit and in the goals. If he does West Ham's season will only go from strength to strength.
4) Patience is the key to healing Hammers' indifferent home form
Before the Chelsea game West Ham had only won one of them four home games after defeats to Leicester City, Bournemouth and a draw with Norwich City. Bilic identified his side's impatience as the key factor saying they must stop treating home games like basketball matches if they were too enjoy more success in their last ever season at the Boleyn Ground. And that's exactly what they did against Chelsea. The Blues sat deep initially but West Ham were patient in the second half when Chelsea were down to 10. They probed and kept the ball and waited for the opportunity and took it when it came with Carroll heading home the winner.
5) Kouyate the unsung hero
All the headlines this season, justifiably, have gone to the likes of Dimitri Payet and Manuel Lanzini. But without Cheikhou Kouyate none of it would work anywhere near as effectively. He was imperious against Chelsea and dominated the midfield battle. His strength, endless stamina, awareness and quality on the ball are so important to West Ham's system. He does a lot of work that goes unnoticed like closing space down, spotting danger early and cutting off supply lines as well as reading the game and making crucial interceptions. He breaks away at pace in his languid style like a modern day Patrick Vieira and the Hammers fans love and appreciate him. Kouyate's work allows the likes of Payet and Lanzini to play and damage the opposition higher up the pitch. He truly is a real beast in the centre of the park.