Tottenham reached the quarter-finals of the EFL Cup after beating Chelsea on penalties following a 1-1 draw on Tuesday.
Timo Werner struck his first Blues goal 19 minutes into the contest at Tottenham Hotspur Stadium and it looked to be enough to send them into the last eight for the 14th time in the past 20 seasons.
However, Erik Lamela, who started as a makeshift striker, drilled past debutant Edouard Mendy to give Spurs a deserved equaliser with seven minutes of normal time remaining.
The first nine penalties of the ensuing shoot-out were converted before Mason Mount clipped the outside of the left post with the 10th, allowing Spurs to progress.
Chelsea made eight changes from their Premier League draw with West Brom on Saturday, handing full debuts to Ben Chilwell and new goalkeeper Mendy, while Harry Kane dropping to the bench was one of nine alterations for Spurs from their draw with Newcastle United.
Sergio Reguilon's debut did not start according to plan, as the Tottenham left-back lost possession and was easily beaten by Cesar Azpilicueta, whose deflected low cross allowed Werner to fire low past Hugo Lloris.
Mendy was also given a busy first half in English football, just managing to stop Gedson Fernandes along with Kurt Zouma and then blocking Lamela's strike with his legs.
Reguilon and Mendy came face to face early in the second half, the Spurs man's stinging strike palmed over the bar after good play from Serge Aurier.
Mourinho threw on Kane with a little over 20 minutes left as Spurs maintained their pressure, but it was Lamela who levelled, slotting low past Mendy after working space from Reguilon's cross.
Eric Dier, Tammy Abraham, Lamela, Azpilicueta, Pierre-Emile Hojbjerg, Jorginho, Lucas Moura, Emerson Palmieri and Kane all scored before Mount's crucial miss, as Spurs avenged their shoot-out defeat in the semi-finals of two seasons ago.
What does it mean? Big opportunity goes begging for Lampard
Mourinho had already effectively written off Spurs' chances in this game, the packed fixture list leading him to prioritise the Europa League play-off with Maccabi Haifa and the league trip to Manchester United later in the week. Chelsea seemed to sense that pessimism early on and were in charge for much of the first half, but their drop-off in standards after the break was inexcusable, even if they too had rotated the side. This competition offered a good chance for Lampard to get his first trophy as Chelsea boss, and this defeat will sting.
Can Lamela lead the line?
If Mourinho is right and injuries continue to plague Spurs, Lamela might just be the surprise solution in a depleted attack. Alongside Steven Bergwijn and then Kane in a front two, Lamela contested 26 duels - over double the number of any team-mate - and won four free-kicks with some fine back-to-goal work. He also took his chance well.
The more things change...
Despite the changes in midfield and to the back four, Chelsea's familiar defensive unease persisted. Spurs started without arguably their four best forwards and still caused plenty of problems, with Zouma and Fikayo Tomori making a few too many last-ditch lunges for comfort and neither able to cut out Reguilon's cross for the equaliser.
Spurs host Maccabi Haifa on Thursday before heading to Old Trafford to face United in the league three days later. Saturday sees Chelsea meet Crystal Palace at Stamford Bridge.