Ross Barkley missed a late penalty as Chelsea's Champions League campaign under Frank Lampard began with a 1-0 loss to Valencia in Group H.
Valencia's off-the-field issues have overshadowed its on-field exploits since Marcelino's sacking last week, but Albert Celades' side bounced back from a 5-2 defeat to Barcelona with a resilient performance at Stamford Bridge.
With Jasper Cillessen in fine form and Mason Mount's injury having compounded Chelsea's frustrations, the Blues' frailties were exposed once more when Rodrigo Moreno prodded in Dani Parejo's free-kick with16 minutes remaining.
VAR came to Chelsea's rescue when the referee decided to award the hosts a spot-kick for a Daniel Wass handball, but substitute Barkley - who overruled Willian to take the penalty - struck the bar.
Fresh from his hat-trick against Wolves, Tammy Abraham should have done better in the sixth minute when he latched onto Cesar Azpilicueta's cross - Cillessen making the save.
Chelsea was dealt a blow soon after, Mount's Champions League debut cut short as he failed to overcome an ankle injury inflicted by Francis Coquelin's robust challenge.
Willian's volley drew a brilliant stop out of Cillessen on the stroke of half-time and Valencia's goalkeeper had more work to do when he kept out Marcos Alonso's free-kick.
But just after Lampard had gambled in throwing on Olivier Giroud for Kurt Zouma, Valencia struck.
Having stole a march on his markers, Rodrigo just managed to make enough contact on Parejo's superb pass.
Chelsea's forutnes looked to have turned with four minutes remaining when referee Cuneyt Cakir handed them a lifeline having looked at the touch-line screen, but Barkley failed to keep his composure.