Chelsea versus Arsenal is always a massive occasion, but Saturday's clash is even bigger than usual because it could be a defining game for both teams.
Jose Mourinho's side have made a horrific start to their title defence, but they will look at this match as a way out of their nightmare and a chance to get their season started properly.
A win, no matter how they get it, would give the defending champions a shot in the arm and deflect the pressure from Mourinho on to Gunners boss Arsene Wenger.
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On the other hand, if his side beat Chelsea it would cause them huge damage - another defeat would leave their Premier League campaign in ruins.
Where will the game be won and lost?
Francis Coquelin. When you look at the group of players Wenger has got to choose from, Francis Coquelin has now become almost irreplaceable because they do not have anyone else who can do his job as a disciplined defensive midfielder.
Francis Coquelin has now become key because they do not have anyone else who can do his job as a disciplined defensive midfielder. Missing out on Morgan Schneiderlin, who joined Manchester United in the summer, looks like an even bigger blow now.
If Coquelin can't protect Arsenal's back four, then Mourinho's men will surely have a field day.
Next is Arsenal's squad depth. In Zagreb on Wednesday night, Wenger's side were starting a run of four away games in 11 days and clearly he had to use his squad and make some changes.
But it stuck out like a sore thumb that Mikel Arteta and Mathieu Debuchy, in particular, were not up to it. They have not played enough football recently, and they were not equipped for the task.
You could say that some of Arsenal's players let Wenger down because he has trusted his squad.
The question is, do Arsenal have enough depth in all areas to match Chelsea's quality?
Chelsea's situation is different because we know how good this team can be - they won the title less than four months ago.
Mourinho has been a big part of what has gone wrong for them so far this season, and he seems to have realised that.
The Blues chief has been a bit too demanding of his team. There is a fine line between encouraging players and wringing a little bit extra out of them, and undermining them by creating too much intensity.
Whatever happens at the Bridge early Saturday afternoon, no doubt it will go a long way to deciding both sides' fate this season. Can Chelsea turn their season around and can Arsenal finally challenge for a title and match the big teams in the big games?