Huddersfield Town secured their Premier League status and dented Chelsea's top-four hopes with a 1-1 draw at Stamford Bridge.
Although Marcos Alonso cancelled out Laurent Depoitre's opener, the Terriers held on for the point they needed to move four clear of the bottom three.
Chelsea could have taken the lead on 12 minutes but from three yards out Antonio Rudiger failed to turn in a flick-on of a corner.
Depoitre made them pay on 50 minutes. He collected Aaron Mooy's long ball, chipped over Willy Caballero and slotted into an empty net.
The Blues equalised 12 minutes later when Zanka's clearance of Cesar Azpilicueta's cross hit Alonso and deflected in.
But despite a crazy goalmouth scramble in which Jonas Lossl tipped Andreas Chistensen's header against the post, Chelsea could not find a winner.
They are two points behind Liverpool, who dropped to fourth following Tottenham Hotspur's 1-0 win over Newcastle United that confirmed Spurs' UEFA Champions League qualification.
See: Chelsea report | Huddersfield report
Next fixtures
Chelsea: 13 May v Newcastle (A)
Huddersfield: 13 May v Arsenal (H)