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 in second place in Group H, two points behind Ajax, who beat Lille 2-0.
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.
"We nearly won it, nearly lost it. It was end-to-end, not that we wanted it to be," said Lampard. "It keeps it in our hands and we have to be happy with that.
"They were arriving in our box too much. Credit to the players for their work-rate and hanging on in there, but sometimes you have to be more secure than that."
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.
"In a very open game in which we've both had chances, we had by far the clearest chances, on top of the penalty," said Valencia coach Albert Celades. "The key was that we didn't take them."
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.
Abraham was then left wincing in pain and holding his left hip as he was trampled on inside the area and eventually had to be stretchered down the tunnel after both sides had already made their way to the dressing room at half-time.
"He's had a bang on the hip but it might not be as severe as we first thought," said Lampard, who confirmed the England international has not gone to hospital.
Despite the loss of their key marksman, Chelsea took the lead five minutes into the second period when Pulisic kept up his fine scoring form by prodding home Kurt Zouma's knockdown.
Following a lengthy VAR check for offside, the goal was given, but Valencia were furious there was not a check for a potential foul by Zouma in the build-up.
The hosts still only had themselves to blame for not getting all three points as Rodrigo chipped over with the goal gaping after Kepa scampered from his goal to clear and was caught in no man's land.
Kepa made amends 25 minutes from time with a brilliant save from Parejo's penalty after Jorginho was harshly penalised for a foul on Jose Luis Gaya.
The drama did not end there, though, as Wass's overhit cross smashed off the far post and into the Chelsea net eight minutes from time.
And Valencia should have gone onto win it as in six minutes into stoppage time Rodrigo somehow prodded wide from Gaya's cross with the whole goal to aim at.
Instead Celades's men now need to win in Amsterdam on December 10 to go through.
"I have to highlight the ambition of the team," added Celades.
"At 2-2 we went for the win to qualify us despite the risks, because if we had lost we would have to thrash Ajax to go through."