Albion have drawn four of their last five matches against Chelsea.
Leandro Trossard takes the ball round Kepa to put Albion in the lead after five minutes.
Loftus-Cheek deflects March's corner past Kepa, before Thiago Silva does the same from Estupinan's cross.
Havertz pulls one back early in the second half, nodding in from Gallagher's cross.
Pascal Gross grabs Albion's fourth as he fires home from close range, after Mendy saved Enciso's strike.
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