Inter Milan lost 4-3 to Atalanta in Serie A after leading 3-1 with less than half an hour remaining. Elsewhere, title-challengers Napoli closed the gap to league leaders Juventus to nine points.
At the San Siro, striker Tommaso Rocchi made the most of a rare start for Inter by putting the hosts ahead in the 43rd minute. But in a second half it was a case of tit-for-tat as both sides went on a 20-minute, six-goal scoring spree.
Giacomo Bonventura levelled for Atalanta on 56 minutes, only for Ricardo Alvarez to restore the Nerazzurri's lead a minute later. Four minutes later Alvarez struck again to give Inter a two goal cushion, only for Denis to level from the penalty spot on 65 minutes.
Denis grabbed his second six minutes later and completed his hat-trick in the 77th minute to give the Bergamese side a shock 4-3 lead. Inter should have levelled at the death however defender Andrea Ranocchia somehow skewed the ball high and wide only two metres out with the goal at his mercy.
Title-challengers Napoli closed the gap to Serie A leaders Juventus to nine points thanks to a 2-0 win over Genoa at the San Paulo.
Juve sit top with a nine-point on Napoli with Milan still in third but four points off second place after giving up a two-goal lead in a 2-2 draw away to Fiorentina.
Fiorentina sit fourth, six points further off the pace but two ahead of Lazio ahead of the 'Derby della Capitale' on Monday away to Roma, with Inter sixth, also on 50 points.
Genoa gave Napoli a scare after just two minutes when Andrea Bertolacci unleashed a shot which Morgan De Sanctis did well to parry. However that was just about all the visitors had to offer in the opening half as Napoli took control on their way to a 2-0 half-time lead.
Pandev threatens, Napoli dominate
Genoa goalkeeper Sebastien Frey, who later saved a penalty from Edinson Cavani, did well to parry from Goran Pandev's drive and the forward threatened again ten minutes later when he cut inside to unleash a shot that went inches past the upright.
Pandev made no mistake minutes later with Cavani's pass after the Uruguayan had won the ball back just outside the area, controlling well before firing home off the underside of the crossbar.
Cavani turned provider again on the half hour, this time feeding Marek Hamsik in midfield before the Slovakian found Blerim Dzemaili unmarked to the left of goal and free to send a low strike under Frey.
Napoli resumed in similar fashion after the break, but opportunities from Cavani, Hamsik and Pandev all failed to hit the net as Genoa reinforced at the back.
Earlier, ten-man Fiorentina scored two late penalties in a 2-2 draw at home to AC Milan to dent the Rossoneri's bid for a second place finish in Serie A.
Milan took a deserved lead in the 14th minute thanks to former Viola midfielder Riccardo Montolivo and were given a further boost when Nenad Tomovic saw red on 39 minutes for an apparent elbow to the face of Stephan El Shaarawy.
The visitors doubled their lead just after the hour thanks to Frenchman Mathieu Flamini, only for Adem Ljajic and David Pizarro to score one each from the spot in the closing stages to earn a share of the points.
There was a new twist in the battle to avoid the drop as Siena and Palermo joined Genoa in a three-way tie for 17th place. The Ligurians' defeat at Napoli saw them drop to second from bottom on goal difference with the Bianconeri and Rosanero matching them on 27 points thanks to mixed results.
Siena's point came from a goalless home draw with Parma, who remain tenth, while Palermo pulled off a surprise 3-1 win at Sampdoria. Steve Von Bergen scored first at the Marassi with Josip Ilicic and Santiago Garcia making Gianni Munari's effort for Samp an irrelevance.
The win was Palermo's first away from home since victory at Bologna in April last year and increases their chances of remaining in the top flight for a tenth consecutive season. Antonio Di Natale, meanwhile, returned to scoring form as his two goals guided Udinese to a 3-1 win over 16th-placed Chievo.
Di Natale scored twice in five first-half minutes before Paul Papp pulled one back, only for Mehdi Benatia to seal victory at the death. Udinese remain ninth, one point behind Catania, who were held to a goalless draw in Sicily by 11th-placed Cagliari.