Roma dropped out of Serie A's Champions League places on Sunday after falling to a shock 4-3 home defeat to Sassuolo.
Roma could have moved level on points with second-placed Inter Milan who lost at struggling Spezia on Friday but were stunned by an Armand Lauriente double, Domenico Berardi's penalty and Andrea Pinamonti's neat finish with 15 minutes remaining.
Roma were without the suspended Jose Mourinho and had to play the entire second half a man down after Marash Kumbulla was sent off for kicking Berardi and conceding the spot-kick from which the Italy international gave Sassuolo a two-goal half-time lead.
Mourinho's team, who netted through Nicola Zalewski, substitute Paulo Dybala and Georginio Wijnaldum, are now fifth, level on 47 points with fourth-placed AC Milan but below the champions by virtue of having played a game more.
There is little chance of Roma moving back into the top four as Milan host Salernitana on Monday night.
Mourinho was absent after his two-match ban for being sent off during Roma's defeat at Cremonese earlier this month was confirmed.
Roma are livid at the decision as Mourinho's red card came following a blazing row with fourth official Marco Serra, who, the capital club claim, insulted their Portuguese coach.
Home fans waved hankies in a Spanish-style protest before kick-off while Roma decided on a media blackout for both Sunday's match and next weekend's Rome derby.
A Roma team missing Italy internationals Lorenzo Pellegrini and Andrea Belotti to injury and Bryan Cristante to suspension got made an awful start.
They gave away two cheap goals to Lauriente in the first 18 minutes.
Zalewski pulled Roma back into the game midway through the first half with a volley which bounced fortuitously over Andrea Consigli.
Kumbulla's daft reaction on the stroke of half-time presented Berardi with Sassuolo's third.
Roma were forced to bring on Dybala, being rested ahead of the trip to Real Sociedad in the Europa League last 16 on Thursday. Even though the Argentina forward did crash in his team's second in the 50th minute there was no stopping Sassuolo.
Pinamonti dinked home a lovely finish after being sent through by the lively Lauriente. Wijnaldum's first Roma goal was scant consolation.
Earlier Verona's survival bid stalled after a 1-1 draw with Monza left them five points from 17th-placed Spezia and safety.
Simone Verdi's 51st minute opener for the hosts was almost immediately cancelled out by Stefano Sensi's tap-in from Carlos Augusto's pull-back.
Verona were saved from defeat when their former star Gianluca Caprari was denied a winner for Monza after Andrea Petagna was millimetres offside in the build-up.
Fiorentina beat bottom team Cremonese 2-0 to win their fifth straight match.
