Juventus's hopes of dropping Inter Milan virtually out of the Serie A title race were ended after the champions suffered a shock 2-1 home defeat to Sampdoria on Sunday.
Inter had been stunned 3-0 by Udinese in Sunday's early match, handing Juventus the chance to take their lead over the Nerazzurri -- widely considered Juve's main title rivals -- to a massive 12 points.
But after Sebastian Giovinco had given the Bianconeri a 24th minute lead from the penalty spot the hosts were stunned by a double from Argentine striker Emanuel Icardi in the 52nd and 68th minutes.
Giovinco stepped up to convert Juve's penalty with relative ease after Claudio Marchisio was adjudged to have been fouled in the box.
But Sampdoria came fighting back in the second half and when Icardi broke free in the 52nd minute he beat Gianluigi Buffon with an impressive angled strike from the edge of the area.
Italy 'keeper Buffon was then left clutching at thin air when, from a tight angle, the Argentine blasted the ball inside the near post and into the roof of the net on 68 minutes.
Sampdoria held on to record a famous win at Juventus Stadium and hand the champions only their third defeat of the season, which will be seen as a missed chance to leave Inter behind for good.
At the halfway stage champions Juventus, on 44 points, now have a five-point lead over Lazio, who secured a late 2-1 win over Cagliari on Saturday.
Fiorentina, in third, had hoped to close the gap to Lazio to one point, as well as further distance fourth-placed Inter only to suffer a shock 2-0 defeat at home to visiting Pescara.
AC Milan, who hit the headlines midweek after midfielder Kevin-Prince Boateng led his team off the pitch during a friendly to protest racist chants from fans of fourth division side Pro Patria, secured a precious 2-1 win at home to Siena.
Milan were whistled off the pitch after a scoreless first half, but Boateng provided the cross for Spain international Bojan to head their opener just after the hour mark.
Giampaolo Pazzini stepped up to convert a penalty in the final 10 minutes, but Michele Paolucci made it a nervy finish for Massimiliano Allegri's men at the San Siro when he reduced arrears in the closing minutes.
Milan held on to remain in seventh and sit two points behind Roma, who visit Napoli later Sunday needing a win to leapfrog the Partenopei into fifth place.
Elsewhere, Chievo secured a precious 1-0 win over Atalanta to leapfrog the Bergamo side into 11th while Genoa moved away from the relegation zone thanks to a Marco Borriello double in a 2-0 win over Bologna.
Parma moved up to eighth, meanwhile, after Amauri's winner in injury time secured a 2-1 win over visiting Palermo, who had levelled Ishak Belfodil's opener for the hosts thanks to Igor Budan's 85th minute header.