Chelsea mounted a stirring fightback from 4-1 down to earn a crucial Champions League point as Ajax ended with nine men on a night of high drama at Stamford Bridge.
The Dutch champions, semi-finalists last season, were in calm control and looked on course for victory when Donny van de Beek gave them a three-goal lead 10 minutes after the break - but in a chaotic closing period Chelsea completed a remarkable recovery as the visitors lost their discipline.
Having pulled one back through Cesar Azpilicueta's close-range finish to make it 4-2, the game turned on its head in 60 seconds of high drama in the 68th minute.
Daley Blind fouled Blues striker Tammy Abraham, referee Gianluca Rocchi allowed play to continue and a shot then hit Joel Veltman's arm in the 18-yard box. Rocchi awarded a penalty, went back and showed Blind a second yellow card, with fellow centre-back Veltman also sent off seconds later for the handball.
Jorginho scored from the spot for the second time in the game to set up a frantic finale.