After the thrilling fare between the two sides at Stamford Bridge, the one-sided nature of the return, which saw Chelsea suffer their biggest defeat under Antonio Conte since their 3-0 loss at Arsenal last season, was a sign of unsettled times for the Italian.
Yet it took no time for the duel to explode into life again.
When Aleksandar Kolarov’s hoofed ball from the left flank was nodded back a mite fortuitously by Edin Dzeko in Roma’s opening foray, El Shaarawy was on to the loose ball in a flash to send his right-footed shot on the half-volley crashing past Thibaut Courtois.
Chelsea countered brightly with Eden Hazard causing problems for the home rearguard, Alvaro Morata hooking one shot over from close range and Tiemoue Bakayoko heading just wide.
Yet when the former Roma man Rudiger had a lapse of concentration at the back, allowing El Shaarawy to pounce on a speculative ball forward from Radja Nainggolan and nudge his effort expertly past Courtois, Chelsea’s poise disintegrated.
Most shocking for Conte was just how tamely his side capitulated after the break, looking nothing like the team which looked so solid throughout their Premier League title-winning campaign.
Cesc Fabregas, in his 100th Champions League match, typified the malaise by giving the ball away to kick start the move that saw Perotti strike a fierce 25-metre shot past Courtois.
The Argentine should then have made it four but ballooned his shot high and Courtois had to make two fine saves in a minute, including a dazzling stop at point blank range from substitute Kostas Manolas, to spare Chelsea further indignity.
The Premier League side’s only consolation after their nightmarish Halloween performance was that they were still effectively in control of their destiny after Atletico Madrid’s surprise draw with Qarabag.
(Reporting by Ian Chadband; Editing by Toby Davis)