Nicolas Jackson was sent off four minutes after coming on as a substitute as Chelsea suffered a second-half collapse against Flamengo at the Fifa Club World Cup.
The Blues led through Pedro Neto but conceded twice and lost Jackson to a red card in a disastrous six-minute spell after half-time.
Neto's cool finish under the goalkeeper's legs delivered a positive start for the Premier League side but similar far post tap-ins from substitute Bruno Henrique and Danilo allowed the Brazilian team to take the lead.
Referee Ivan Barton then quickly issued a red card after Jackson's studs made contact with Lucas Ayrton's shin in an ugly challenge with Wallace Yan rounding off the scoring to deliver a damaging 3-1 defeat to Chelsea.
It leaves the Blues needing a win over African club ES Tunis on Tuesday to qualify for the last 16 but also increases the chances they will face the winner of Group C, which could be Bundesliga giants Bayern Munich.
Flamengo, meanwhile, look likely to finish top of Group D and have ensured South American clubs remain undefeated in the newly-expanded Club World Cup.