Chelsea saw safe passage to the Champions League knockout stages slip agonisingly away as Daniel Wass' fluke stole Valencia a 2-2 draw at the Mestalla.
England striker Tammy Abraham was taken to hospital after a nasty-looking fall on a night where the Blues thought Christian Pulisic's nudged finish would sneak them into the European top tier's last 16.
Abraham suffered a suspected internal injury after falling awkwardly on his hip, no doubt adding to boss Frank Lampard's frustrations as Valencia gained the greater boost in Group H from the draw.
Mateo Kovacic fired his first Chelsea goal on his 71st Blues appearance, cancelling out Carlos Soler's opener.
Jorginho was lucky to escape a second yellow card and a dismissal for the foul on Jose Gaya that gifted Valencia a second-half penalty. Captain Dani Parejo stepped up for the spot-kick only to see Kepa Arrizabalaga pull off a fine save.
Maxi Gomez missed a hat-trick of first-half sitters as Valencia paid the price for shocking profligacy, but just when Chelsea started to home in on victory up popped Wass.
The Denmark midfielder's lofted cross drifted away from his intended target but instead over Kepa and into the net, stealing Valencia a draw to thwart Chelsea at the last.
Rodrigo's glaring miss at the death could even have sealed Valencia's place in the last 16, but a compelling, gritty game somehow ended even.
Victory here would have sent Chelsea into the knockout phase with a group game to spare, but now the Blues must wait to secure their passage into the last-16.
"I wouldn't say I feel fortunate, but I didn't really love the match. Both teams had incredible chances, we had numerous ones in the first-half.
"But there haven't been very many times this season where I've had to say 'we kind of got away with that'. It could have been five-all or six-six, it was one of those games. We should be better defensively than we were today.
"I'm happy to a degree, you come here to win but you respect the opponent, the Champions League and how tough it is. It was a really tough match for us but it does keep it (qualification for the last 16) in our hands."