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Chelsea avoided a similar embarrassment to last season's stunning 4-2 FA Cup defeat at home to Bradford City, although at times they made hard work of their tie against another third-tier side in Scunthorpe.
Spanish international Diego Costa put them ahead in the 13th minute from a cross by Branislav Ivanovic.
But the visitors rallied well in the second half and were furious to be denied a penalty when Ramires appeared to trip Kevin van Veen.
A few minutes later 19-year-old Londoner Ruben Loftus-Cheek, a half-time replacement for Oscar, scored his first goal for the club from Cesar Azpilicueta's low centre.
Scunthorpe were denied a consolation goal when fullback Jordan Clarke's fierce shot struck the post.
But who was their star player at Stamford Bridge? See below for our player ratings...
Chelsea player ratings vs Scunthorpe
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Blues supporters have praised Brazilian winger Willian once again after another sparkling display against their lowly guests.
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