Antonio Conte fiddled but Roma were on fire and Chelsea picked a fine time to spontaneously combust. This was not what Conte had in mind on his first competitive return to the Italian capital.
His team were a goal down in 38 seconds, two down by half-time and trailing by three early in the second-half.
The final score might easily have been more of an embarrassment had it not been for some fine saves by Thibaut Courtois.
Diego Perotti finds the bottom corner for Roma with a shot from distance that beat Thibaut Courtois at his near post
Perotti is mobbed by team-mates after scoring a stunning third goal for Roma after 63 minutes of Tuesday night's game
Stephan El Shaarawy doubles Roma's lead as he gets to the ball before Cesar Azpilicueta and prods it past keeper Courtois
The Italian international has his arms outstretched in celebration after scoring Roma's second goal of the night
Roma's players celebrate as Chelsea boss Antonio Conte watches it all unfold from the touchline with hims arms folded
El Shaarawy gave Roma the perfect start with a goal inside 38 seconds at the Stadio Olimpico on Tuesday night
El Shaarawy pumps his first as Perotti joins him in celebrating his first minute strike against the English champions
Roma (4-3-3): Alisson 6.5; Florenzi 5.5 (Manolas 76), Fazio 6, Juan Jesus 6, Kolarov 6.5; Nainggolan 6.5, De Rossi 7, Strootman 6; El Shaarawy 8 (Gerson 75), Dzeko 7.5, Perotti 7 (Pellegrini 87)
Subs not used: Skorupski, Moreno, Under, Gonalons
Goalscorers: El Shaarawy 1, 36, Perotti 63
Manager: Eusebio di Francesco 7
Chelsea (3-4-3): Courtois 7; Cahill 5 (Willian 56, 5), Luiz 5, Rudiger 5; Azpilicueta 5, Fabregas 5.5 (Drinkwater 71, 5), Bakayoko 5, Alonso 5; Pedro 6, Morata 5 (Batshuayi 75), Hazard 6.5
Subs not used: Caballero, Kenedy, Zappacosta, Christensen
Manager: Antonio Conte 6
Referee: Jonas Eriksson 6
Stephan El Shaarawy scored the first two, both brilliantly finished yet so poorly defended by Chelsea, who simply could not contain the threat of Edin Dzeko for the second time in this European campaign.
There are injuries in key areas of the squad eating away but it is hard to equate this display with the unit Conte had so well-drilled last season.
From the first minute to the last they were devoid of shape and composure at the back and poorly protected in midfield.
For good measure, they were wasteful up front but defensively they were brutally exposed by Roma who have plundered six in 180 minutes against Chelsea.
Diego Perotti grabbed the third before missing the clearest chance of the game, firing over when totally unmarked in front of goal.
Courtois stopped Roma running riot, including one fabulous reflex save to deny Kostas Manolas from close range. It was so good that Manolas shook the goalkeeper by the hand.
Chelsea remain well placed to qualify the last 16, mainly thanks to Atletico Madrid's inability to beat Qarabag, the unfancied minnows from Azerbaijan.
'The second-half was really bad,' said Conte. 'Roma showed more desire to first and win the game. I am disappointed for our second half. We all have to take the responsibility.
'When you concede three goals you need to be worried because it means something doesn't work. It's very difficult to tell what this is but for sure we have analyse the game and we need to work on the tactical aspect.'
But their careless habits at the back will infuriate Conte's attempt at another defensive shuffle, swapping Gary Cahill to the right and Antonio Rudiger to the left and moving Cesar Azpilicueta to wing-back, again, soon backfired.
Cesc Fabregas gets his foot on the ball and looks to find another Chelsea shirt in the early stages of the match
Eden Hazard passes the ball forward as Chelsea look to find a way back into the match after going behind early
Antonio Conte appeals for a decision to the referee as Cesar Azpilicueta battles for possession on the touchline
Chelsea defender Marcos Alonso tries to keep an eye on Roma forward El Shaarawy during the first half in Rome
Chelsea midfielder Tiemoue Bakayoko chases after the ball as Roma skipper Daniele De Rossi looks to take control
Roma midfielder Radja Nainggolan tugs on the shirt of his opponent and Belgian team-mate Eden Hazard
They failed to cope with Roma's first attack of the game, a long diagonal pass from Aleksandar Kolarov to Dzeko.
Dzeko could not make the contact he wanted as he twisted in the air but still managed to nod the ball into the path of El Shaarawy who applied a searing strike with the outside of his right boot.
Francesco Totti, gazing down in imperial fashion from the VIP seats, would have approved. After their performance at Stamford Bridge, there was an air of confidence about Eusebio di Francesco's team.
Clearly, they thought Chelsea were there to be got at and here was further evidence. Without Azpilicueta in the back three and N'Golo Kante in midfield the Premier League champions are not nearly as solid as they can be.
Kante has been out for nearly a month with a hamstring injury sustained on international duty with France. He has been back in training since Friday and travelled with the squad to Rome but he was not even on the bench.
'It's not right to push,' said Conte. 'The player must have the right feeling.'
Match referee Jonas Eriksson points as he makes a decision while Chelsea star Cesc Fabregas gestures to a team-mate
Belgian star Eden Hazard lets out a cry of anguish as Chelsea struggle to assert themselves on the game in Italy
Marcos Alonso is sent flying into the air after a collision with Roma defender Federico Fazio in the opening period
Roma's players look to get a head on the ball as it is swung into their penalty area by an opposition player on Tuesday night
His continued absence meant Tiemoue Bakayoko was in tandem in the centre of midfield with Cesc Fabregas, who was making his 100th Champions League appearance.
At the back, they were vulnerable, often hustled into mistakes on the ball in dangerous areas when Roma chose to exert pressure but at least in the first-half Conte's team carried a threat when they went forward.
Eden Hazard, released by Fabregas, squandered a terrific chance to level soon after the opener but his finish was tame. Certainly, it did not match the electric burst of speed which took him away from the back four and his effort was easily saved by Alisson.
Twice in quick succession Hazard forced Alisson to make low saves and Alvaro Morata missed the target as he tried to clear the Brazilian 'keeper after Pedro charged down an attempted clearance from Kolarov.
Chelsea's gathering momentum stalled when Hazard was hurt by Alessandro Florenzi stepping on his heel from behind. The stoppage was soon followed by a lapse in concentration from David Luiz as he tried to control a high ball.
Chelsea striker Alvaro Morata trudges back to the half-way line with a mountain to climb after El Shaarawy's second goal
Roma midfielder Kevin Strootman leaves Fabregas for dead as the home side click through the gears in the second half
Courtois made the save, blocking from El Shaarawy and cleared the corner which followed but the Londoners were still out of sorts when Radja Nainggolan tested their defensive capabilities with another long pass from the left.
Rudiger seemed set to tidy it up but dithered and allowed it to bounce, while Azpilicueta was beaten in a sprint by El Shaarawy, who poked at a shot with his right foot to beat Courtois.
Still, Chelsea enjoyed good chances to reduce the deficit. Alisson saved from Marcos Alonso and Bakayoko headed wide from a corner.
Early in the second half and Conte replaced captain Cahill with Willian. Cue more shuffling around but no sooner had Pedro shifted into the role of wing-back than Perotti glided inside and sent a third skidding past Courtois from the edge of the penalty area.
Chelsea's attacking threat faded after the break. They were on the back-foot, striving to keep the score down and Conte's substitutions did nothing to change that.
Back in the Italian capital, he came, he saw, he conceded three just as Luiz Felipe Scolari did when Chelsea were beaten here 3-1 nine years ago. And he flew home with some serious work to do before Manchester United on Sunday.
Roma boss Eusebio Di Francesco embraces Chelsea manager Conte in the technical area before kick-off on Tuesday night