Lazio's recent revival came to a grinding halt with a 2-0 humiliation by Genoa at the Olympic Stadium as Inter Milan put three unanswered goals past Udinese on a rain-hit trip north.
Elsewhere, Domenico Berardi made it a Sunday to remember for Sassuolo, the striker scoring a hat-trick, including a late penalty, to help the Serie A new boys dominate a seven-goal thriller away to struggling Sampdoria.
Verona meanwhile continued their strong start to the campaign with a 2-1 win at home to Cagliari which moved the newly-promoted side up to fifth at the expense of Fiorentina, 2-0 winners over AC Milan at the San Siro on Saturday.
Vladimir Petkovic's men looked to have put a recent slump behind them with a home win over Cagliari and a draw away to Milan in the past ten days.
However the Biancocelesti paid the price for missing several chances in the first half when Juraj Kucka broke the deadlock on the hour and Alberto Gilardino doubled the visitors' lead 12 minutes later from the spot.
Lazio's fourth reverse left them in seventh, 15 points behind Roma and seven adrift of Verona.
Verona started strongly and took an eighth-minute lead when Luca Toni was left alone by the Cagliari defence to nod past Michael Agazzi in the Cagliari net.
Bosko Jankovic doubled the hosts' lead on 57 minutes and Verona survived a nervous finish after Daniele Conti's 90th minute strike to claim a seventh win in 11 games to go fifth, only eight points shy of Roma.
Udinese's Friuli Stadium is known as a difficult venue for visiting teams but two weeks after a 1-0 defeat to Roma, Francesco Guidolin's side buckled again under a far more clinical Inter side.
The visitors opened the scoring through Rodrigo Palacio in the 25th minute when the Argentine flashed a header past goalkeeper Zeljko Brkic from close range following Saphir Taider's precision free kick.
Four minutes later Brkic dashed out of his goal in wild fashion to intercept a corner kick that was out of his reach and Inter defender Andrea Ranocchia volleyed the ball through traffic and into a virtually empty net.
Colombian Muriel spurned the chance to reduce arrears when he pounced on a blunder by Inter defender Walter Samuel. Instead of feeding fellow striker Antonio Di Natale who was unmarked to his right, he sent a wild shot across the face of goal.
Udinese, who finished fifth last season, now sit in tenth at 18 points adrift of Roma, who dropped points for the first time this season with a 1-1 draw at Torino. Kevin Strootman had the Serie A leaders ahead in the 28th minute, but Alessio Cerci leveled matters for the hosts midway through the second half.