Napoli stun Juve to spark life into title race
Napoli's forward Jose Maria Callejon celebrates after scoring during an Italian Serie A football against Juventus at San Paolo Stadium on March 30, 2014 - by Carlo Hermann
Juventus had seen their 14-point lead cut back earlier in the day when Roma, in second with a game in hand, prevailed 2-0 at struggling Sassuolo.
Napoli came flying out the blocks and at the tail end of a dominant first half Callejon broke the deadlock in the 37th minute.
The pace slowed somewhat after the break but moments after replacing Slovakian Marek Hamsik, Mertens made the most of Goran Pandev's delivery to beat Gianluigi Buffon with a crisp drive from the edge of the area and condemn Juventus to just their second league defeat of the season.
Juve now lead Roma by 11 points with Napoli, who have been chasing the second automatic Champions League qualifying spot, still third but six points behind Roma.
Striker Gonzalo Higuain returned to Rafael Benitez's starting Napoli line-up after being rested for the 4-2 win at Catania in midweek, while Pablo Daniel Osvaldo replaced the suspended Carlos Tevez to partner Fernando Llorente in Juve's attack.
The statistics, however, were all in favour of Juventus, who were unbeaten in their last six encounters with Napoli and had restricted the hosts to only one goal in their last four games.
Napoli enjoyed the early pressure with Buffon pulling off a great reflex save in the seventh minute to stop Callejon from close range and the Spaniard tested the 'keeper again on the half hour when he picked up Lorenzo Insigne's cutback after it missed Higuain.
Juve were seeing little of Pepe Reina's goal but Llorente failed to make contact with Stephan Lichsteiner's probing cross on the half hour.
Minutes later, Napoli took advantage of Kwadwo Asamoah playing in a makeshift defensive role, Callejon ghosting in behind the Ghanaian midfielder to meet Lorenzo Insigne's cross to beat Buffon from close range.
At the other end a spectacular bicycle kick from Osvaldo from Lichsteiner's delivery was well over the bar.
Asamoah made way for Mauricio Isla eight minutes after the restart and the Chilean almost made the difference immediately when he controlled well on the right to cross for Osvaldo, but Reina got down low to block.
On the hour, Hamsik won a free kick when his feint prompted Leonardo Bonucci to foul on the edge of the area and once again Juve had Buffon to thank for tipping Faouzi Ghoulam's well-struck effort to safety.
Juve coach Antonio Conte shook things up when he replaced Paul Pogba with Claudio Marchisio and minutes later Osvaldo made way for Mirko Vucinic.
Vucinic had to wait only moments before having a shot on goal when he collected Arturo Vidal's short pass on the edge of the area only to curl wide of Reina's upright.
With legs tiring, Higuain came off for Goran Pandev in the 73rd minute and Napoli had Ghoulam to thank when he ran back to block Isla as he teed up a shot to the right of goal following Vucinic's through ball.
At the other end Hamsik was sent through by Pandev but Buffon had no trouble getting low to block the Slovakian's tame shot from the edge of the area.
Hamsik made way for Mertens in the 78th minute and moments later the Belgian made no mistake when Pandev picked him out with a smart pass to beat Buffon with a crisp angled strike.