They not only have to stop the Blues scoring and become the first side since Sunderland to do so, but they will also need to find their way past a mean Chelsea defence that boasts one of the tightest records not to mention the best goalkeeper in the league behind them – and that applies no matter who out of Petr Cech or Thibaut Courtois gets the nod.
The Blues are on a roll after winning the League Cup and Jose Mourinho will want to show nothing is slipping domestically – and Sam Allardyce knows his side are in for a battle.
With that in mind, here are five key clashes the Hammers have to win should they hold out any hope of beating the Blues.
Click on Enner Valencia to see who we think has to come out on top for the home side.
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