A hat-trick by Croatia striker Nikola Kalinic set up Fiorentina for 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 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.

Fiorentina were gifted the perfect start when the referee pointed to the penalty spot after Handanovic impeded Kalinic in the area.

Josip Ilicic stepped up to slam the ball into the roof of the net after just four minutes.

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 defense.

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.