Icardi played a season in Serie A with Sampdoria after coming through their youth ranks but he showed no sign of going easy on his former club.
The Argentine, who has been left out of his national side's squad for this round of games, scored a 14 minute hat-trick before half time and added another after the break.
Ivan Perisic got the first for the 'Nerazzurri' with a clever looping header from Cancelo's cross before Icardi took over.
Rafinha was fouled in the box and Icardi bagged his first in the 25th minute from the spot. The second came only three minutes later, Icardi backheeling the ball across the line after the keeper fumbled. With half an hour gone, Inter were three to the good and out of sight.
But there was still time for one more in the first half, Icardi smashing into the roof of the net after another defensive error.
After the break he continued where he left off, scoring in the 51st minute with an effort that bounced high and over the goalkeeper. 5-0 was how the scoreline finished, Icardi taking home the matchball and another goal to boot.
The win lifted Inter above Lazio into 4th and put the pressure on cross city rivals, Milan, who play Chievo later on Sunday.
18 March 2018