A hat-trick by Croatia striker Nikola Kalinic inspired Fiorentina to a stunning 4-1 win at the San Siro that ended Inter Milan's 100% start to the campaign and sent La Viola top of Serie A for the first time in 16 years on Sunday.

Inter, who have not won the scudetto since their treble-winning feat of 2010, had boosted their early-season hopes by racing to a 10-point lead over defending champions Juventus after winning their opening five games.

Juventus were at risk of being left 13 points in arrears but a stunning first-half performance from Paulo Sousa's visitors, who had raced to a 3-0 lead by the interval, served a stern reminder that the Serie A season is far from over.

Inter had conceded only one goal in their opening five games but by the 23rd minute goalkeeper Samir Handanovic had picked the ball out of his net three times.

The bulk of the damage had been done, said Inter coach Roberto Mancini, even before then.

"The penalty at the start changed the whole game for us," Mancini told Mediaset Premium.

"On Ilicic's first shot we conceded the second goal and after Miranda's sending off the game was over.

"From two shots, we were three-nil down. But I have to say well done to Fiorentina, who played well and had control of the game."

It is the first time Fiorentina have been top in Italy since February 1999, when AC Milan went on to beat Lazio to the title.

"The biggest satisfaction is seeing how well the lads played," said Sousa, who was quick to shoot down suggestions Fiorentina would challenge for the title.

"Let's be realistic. There are teams who have a lot more quality and who have invested a lot in players. We have to keep on fighting with the team we have."

Fiorentina were gifted the perfect start when the referee pointed to the penalty spot after Handanovic impeded Kalinic in the area and Josip Ilicic stepped up to slam the ball into the roof of the net on four minutes.

Handanovic admitted he had been at fault on several occasions, but said: "I accept that part of the defeat was down to me, but it should not have been a penalty.

"Kalinic fell to the ground as soon as I touched him, then the sending-off changed everything."

If the early opener shellshocked the Nerazzurri, they were ill-prepared for what was about to follow.

Barely 15 minutes later Handanovic was beaten again, although this time the Slovenian 'keeper could justifiably apportion some of the blame to Inter's sloppy defence.

Handanovic could only parry a powerful dipping drive from Ilicic and as he and Brazilian defender Miranda waited for the ball to land, Kalinic wasted no time in running in to tap the ball home at the near post.

Four minutes later Kalinic had doubled his tally for the night, the Croatian sliding in from close range to meet Marcos Alonso's sweeping drive from the left flank.

By now, Inter were all at sea and their night went from bad to worse on the half hour when Miranda was shown a straight red card for tugging on Kalinic as the striker ran down towards goal.

Coach Roberto Mancini replaced the ineffective Geoffrey Kondogbia at half-time, the French midfielder making way for defender Andrea Ranocchia.

But although Inter reduced the arrears on the hour mark, Mauro Icardi picking up his own rebound from an Alex Telles' free kick to beat Ciprian Tatarusanu, it was a rare bright spot in an otherwise forgettable performance.

Fiorentina looked dangerous on almost every opportunity and Kalinic secured his hat-trick on 76 minutes when he beat Handanovic down low after a superb one-two with Ilicic.

Thanks to La Viola's superior goals difference, they went top ahead of Inter, who also have 15 points, with Torino two points off the pace in third.

Lazio sit fifth, one point ahead of Roma, with champions Juventus in 15th place following a 2-1 defeat to Napoli on Saturday as they reel from their worst start to the season in decades.