Ryan Hardie missed a penalty with two minutes in extra-time remaining as Chelsea held on to edge Plymouth Argyle in the FA Cup fourth-round tie at Stamford Bridge.
Malang Sarr gave the ball away and then brought down the Plymouth substitute who got up to take a weak spot kick which Kepa Arrizabalaga saved diving to his left.
Earlier, Macauley Gillesphey gave the League One outfit a shock lead, flicking home Jordan Houghton's free0kick in the eighth minute.
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Chelsea hit the woodwork on three occasions from Mateo Kovacic, twice, and Callum Hudson-Odoi before equalising four minutes before the break through Cesar Azpilicueta's clever backheel from Mason Mount's cross.
Plymouth were under siege for most of the second half but Michael Cooper was outstanding in the Pilgrims goal and the defenders in front of him ably supported.
However on the stroke of half-time of the added 30 minutes, Kai Havertz exchanged passes with Timo Werner before pulling back for Marcos Alonso to guide home.
This seemed to be the end of the matter but the Blues still needed Kepa to repel Hardie's penalty to stop the game going into a shoot-out.
Eurosport