Daniel Wass's late equaliser denied Chelsea a place in the last 16 of the Champions League as a profligate Valencia fought back for a 2-2 draw that maintains both sides' chances of reaching the knockout stages.
A wide open game swung the visitors' way after Carles Soler's opener for Valencia as Mateo Kovacic and Christian Pulisic put Chelsea in pole position to avenge their 1-0 defeat on home soil to the Spaniards on matchday one.
However, after Kepa Arrizabalaga had saved Dani Parejo's penalty, Wass's cross flummoxed the Spanish international to give Valencia a lifeline.
Both sides are tied on eight points at the top of Group H, but could be overtaken by Ajax who travel to Lille later on Wednesday.
Victory at home to Lille in two weeks' time will ensure Frank Lampard's men make the last 16 and they were thankful to five huge misses from the hosts to escape with a point on a night that could also prove costly as top-scorer Tammy Abraham was stretchered off at half-time.
Maxi Gomez was the principal villain for Valencia as the Uruguayan twice failed to find the net with the goal at his mercy in the first half.
When Valencia did finally break the deadlock there was a hint of fortune in the finish as the ball ricocheted off Soler's legs, but had enough power to beat Kepa.
Defeat would have left Lampard's men on the brink of elimination, but they responded immediately after falling behind as Kovacic produced his first goal for the club at the perfect time with a fine low strike.