Chelsea and nine-man Ajax played out a remarkable 4-4 draw as Frank Lampard's men roared back from 4-1 down and were denied a late winner by VAR.
After winning nine of their last 10 games, including the reverse fixture in Amsterdam, Chelsea were left stunned by last season's semi-finalists as the visitors ruthlessly went 4-1 up inside 55 minutes.
Tammy Abraham netted an early own goal (2) before Jorginho converted from the spot (4) but two goals before half-time from Quincy Promes (20) and another own goal, this time from Kepa Arrizabalaga (35), put Ajax in control while Donny van de Beek (55) extended the lead after the break.
Cesar Azpilicueta started the comeback to make it 2-4 (63) but then a extraordinary six-minute period turned the game on its head when Daley Blind and Joel Veltman were both sent off for second yellow cards, Jorginho scored his second from the spot (71) and Reece James (74) netted an equaliser.
Chelsea thought they had completed the comeback with 12 minutes left but an Azpilicueta strike was ruled out by VAR after Abraham handled the ball in the build-up.
The result means Chelsea, Ajax and Valencia all have seven points with two group games remaining.
Chelsea: Arrizabalaga (6), Azpilicueta (7), Zouma (6), Tomori (6), Alonso (4), Jorginho (8), Kovacic (7), Willian (6), Mount (6), Pulisic (8), Abraham (6)
Subs: James (8), Hudson-Odoi (7), Batshuayi (6)
Ajax: Onana (8), Mazraoui (6), Veltman (6), Blind (6), Tagliafico (6), van de Beek (7), Ziyech (8), Martinez (7), Neres (7), Tadic (7), Promes (8)
Subs: Alvarez (6), Schuurs (6)
Man of the match: Jorginho
How an extraordinary night at Stamford Bridge unfolded
Ajax have still never lost an away Champions League match in England in four previous visits, winning their most recent fixture at Tottenham in last season's semi-final, and started this one full of confidence.
An early period of pressure down Chelsea's right won the visitors a free kick and Promes' quality delivery caught Abraham napping as he diverted the cross into his own net.
Frank Lampard made just one change from the Chelsea side that won at Watford on Saturday as Marcos Alonso replaced Emerson. N'Golo Kante was back on the bench for the Blues after a spell out injured.
For Ajax, in came Noussair Mazraoui and David Neres in place of Edson Alvarez and Sergino Dest.
Chelsea's response was immediate with Christian Pulisic bursting into the box and drawing a late challenge from Veltman which allowed Jorginho the chance to score from the spot, and he didn't pass up the opportunity.
The game continued to flow in entertaining fashion with Hakim Ziyech providing the quality to take the game away from the hosts. It was his magnificent cross from the right that caught out Azpilicueta and allowed Promes to dart in and finish from close range to make it 2-1.
Ziyech's left boot did further damage just before the break as Ajax extended their advantage, although there was a touch of luck about the goal. His delivery from near the corner flag caught Arrizabalaga out and the ball bounced back off the post and into the net via the unfortunate goalkeeper's face.
Things got worse for the Blues when Ziyech found Van de Beek in the area and the classy midfielder found the bottom corner with a clever finish.
Chelsea were still attacking with great tempo despite the deficit and the comeback was started when Abraham's close-range finish was turned home by Azpilicueta at the far post.
Then came the crazy period.
Blind was shown a second yellow card for fouling Abraham and Veltman followed him down the tunnel for handling Callum Hudson-Odoi's shot after the advantage from the Blind foul was played.
Group H table
Jorginho rolled in his second penalty of the night to send Stamford Bridge wild and any fans that left early were made to look foolish as James hammered home from a corner to sensationally equalise.
Azpilicueta thought he netted a dramatic late winner but VAR dampened the celebrations by spotting a handball from Abraham in the build-up while the nine men of Ajax almost nicked it late on but Arrizabalaga kept out Edson Alvarez.
Sky Sports' Nick Wright:
'Some players collapsed to the turf in exhaustion at the final whistle. Others stood with their hands on their hips, dazed and confused by what they had experienced. In the stands, the fans were similarly stunned. This was a game that defied logic. A 4-4 draw that had it all.'
Man of the match: Jorginho
Written off by many at the start of the season, the Italian is fast becoming Chelsea's most important player in the engine room. Once again he was the central cog that knitted everything together for Lampard's side, making the most passes of any player on the pitch (62) with an impressive 92 per cent completion figure. Two of those passes were deemed key, and the way he took his penalties dripped with class.
What the managers said
Cheslea boss Frank Lampard: "Today was just a mad one. I don't think there's too many I can even compare it to from my day.
"I know we had 4-4s with Liverpool and some crazy games, but the red cards and the VAR as well. The VAR is obviously a new animal and we're getting used to that. I'm not the only manager who's talking about it every week. I can't give you any dissection [of those decisions] today because firstly I need to watch it back with a calm head and secondly when you're on the sideline it's very difficult to grasp it straight away.
"Take VAR out of it and the red card and what I think about is us, and the spirit that we showed.
"The character was something that I loved and I think our fans loved. We need to tighten up for sure but with that spirit we can go places."
Ajax boss Erik Ten Hag: "I'm very disappointed. I think we could have had four points from our two games against Chelsea but we only have one.
"Some decisions went against us, but we played magnificently. One momenteverything changed.
"First Daley Blind, then Veltman, and a penalty, I felt we got punished many times."
Debate: Should Chelsea strengthen?
Chelsea Women's manager Emma Hayes reacted to reports that the Blues may spend big in January if their transfer ban is lifted, and although she believes the club would spend if they could, this situation has given youngsters a fine opportunity.
She said on The Debate: "I'm sure he will, when the time is right. There are also senior players who are not starting on a regular basis, who may want to depart.
"The squad number is pretty small at Chelsea, so if the ban is to be lifted, he will have his eye on players, but ultimately he has a group to build around that will be there for years to come.
"Without the pressure of having to sign players, Chelsea are producing players who are proving they are good enough for both the Premier League and the Champions League."
- Chelsea are the third English side in Champions League history to come from three goals behind to avoid defeat and the first since Liverpool in May 2005 (3-3 vs AC Milan).
- Ajax have scored 4+ goals in a game against an English team in all European competition for only the second time (also 5-1 vs Liverpool in December 1966 at home in the European Cup).
- Ajax's opener against Chelsea (1:47) was the second earliest goal conceded by the Blues in the Champions League after Stephan El Shaarawy (Roma) in October 2017 (39 seconds).
Chelsea are back at Stamford Bridge on Saturday as they host Crystal Palace in the early kick-off in the Premier League (12.30pm). In Chelsea's next Champions League tie, they will travel to Valencia on Wednesday November 27.