Chelsea became the first English team to lose a Champions League game this season as they were well beaten by a clinical Roma.
The Blues would have progressed with a victory, but trailed within 39 seconds when Edin Dzeko flicked Aleksandar Kolarov’s cross down to Stephan El Shaarawy, who smashed home from 25 yards.
Alvaro Morata missed a huge chance to equalise from close range, and El Shaarawy made it 2-0 when ex-Roma defender Antonio Rudiger failed to deal with Radja Nainggolan’s long ball forward.
Chelsea had more shots – 14 to 13 – but were three behind when Diego Perotti cracked home from 20 yards after Blues defenders failed to close him down.
Roma should have led 4-0 when Chelsea’s defenders all ran to Dzeko, who managed to square to a totally unmarked Perotti, but he fired over when he should have finished.
The Blues were hugely fortunate that Atletico Madrid’s failure to beat Qarabag – their game in the Spanish capital ended 1-1 – means Chelsea are still likely to qualify for the last 16 from Group C.
Antonio Conte’s side are four points above third-placed Atletico – and a win in their next Champions League game at Qarabag (17:00 GMT on Wednesday, 22 November) will take them through.
In other games, Bayern Munich and PSG progressed to next stage after wins over Celtic and Anderlecht respectively.
Barcelona maintained their unbeaten run as they shared the spoils 0-0 with Olympiacos. Juventus fought back to secure a 1-1 stalemate at Sporting CP while Manchester United won 2-0 over Benfica.
And Basel suffered shock home loss to CSKA Moscow.