And so the streak continues.
This loss made it seven league matches without a win for the Blues, and Rafael Benitez became the first Chelsea manager of the Roman Abramovich era to go winless in his first three games.
Here are six things that we learned from this loss.
Before Roberto Di Matteo left, Chelsea were suffering a dip in form. Since then, it has turned into a full-blown crisis.
Whether you think that Di Matteo was doing a good job or not, the fact is that Abramovich was wrong to sack him.
At such an important stage of the season, Di Matteo had realized that some changes needed to be made and was starting to implement them.
Bringing in a new manager means starting again at square one.
Whether Benitez is the right replacement or not, any manager coming in at such a time is going to struggle and no grace period could be allowed.
Having said that, Benitez was clearly the wrong choice to replace Di Matteo.
Firstly, take a look at the fans' reaction to his appointment.
It is unwise to take a Chelsea alumnus and popular manager, and replace him with a man who had made a name for himself as one of the least popular managers in the eyes of Chelsea fans.
The fans may have forgiven Di Matteo for a bad season. They will never forgive Benitez.
Secondly, take a look at his management record.
In five years at Liverpool, Benitez won two major trophies: the Champions League and the FA Cup. This sounds impressive, until you realize that Roberto Di Matteo, the man that he replaced, did this in a few months with Chelsea.
Benitez then had a successful but brief spell at Inter Milan, followed by a couple of years' unemployment.
Thirdly, take a look at his Chelsea record.
In only three games he has failed to win, dropped Juan Mata for Ryan Bertrand for one game, and started Fernando Torres for each game. He was also clearly outmanaged by Sam Allardyce in this match.
Not a promising start.
The striker has been given chance upon chance to prove that he still has something valuable to give Chelsea. But the time has finally come to accept that he has not—and cannot.
His one assist against West Ham marked his best performance in a Chelsea shirt in 12 hours of league football. And that one assist did not make up for an otherwise poor performance.
Chelsea may not have depth in striking options right now, but they must still find a way to play without Torres.
Chelsea failed to kill the game off when they had the lead in the first half. But any spark of brilliance came from Juan Mata, including the goal.
Many thought Benitez's decision to drop Mata against Fulham bizarre, but after this match at Upton Park, it seems downright ridiculous. Mata must be the man to lead Chelsea forward out of this slump.
With John Terry in the team, Chelsea conceded just four goals in the first seven games. Since then, without him (except 39 minutes against Liverpool), Chelsea have conceded 12 goals in eight games. Three of those were Saturday.
It is clear that Chelsea need their captain leading the defense—or they need someone else to step up in a big way.
In the Premier League title race, Chelsea are now 10 points off the pace set by league leaders Manchester United.
It is a big deficit, but not impossible to make up at this stage of the season.
However, in order for them to make up this deficit, some changes must be made.
Torres needs to be dropped, and Chelsea will need to find one or two good replacement strikers in the January transfer window. The defense needs to put this performance behind them and build off of the two previous clean sheets.
And finally, Benitez needs to start winning.