Icardi had been without a league goal since January 5, but at his old stomping ground he exploded back into life, becoming the sixth-youngest player to reach 100 goals in Serie A and blowing Sampdoria away in an extraordinary performance.
The players ahead of Icardi on the list are: Giuseppe Meazza, Silvio Piola, Giampiero Boniperti, Felice Borel and Jose Altafini all legendary footballers.
180 - Icardi's 100 Serie A goals have come in 180 appearances, for a goals-per-game ratio of 0.56.
The star of the show was former Samp star and Inter talisman Mauro Icardi.
The Nerazzurri extended their solid run of form, which has seen them win three and draw one of their last five games, to climb into the top four. "Clearly it was in my destiny to reach 103 at Marassi".
Ivan Perisic opened the scoring with a looping header in the 26th minute before Icardi, playing against his former club, grabbed a 14-minute hat-trick, the first from a penalty, and added a fourth early in the second half with a mis-hit volley.
Icardi, the 25-year-old Argentina global, who had been sidelined for a month with injury, broke the century after scoring his first goals since January.
The Argentina striker then fooled goalkeeper Emiliano Viviano and defender Gian Marco Ferrari with a splendid backheel goal.
Napoli meanwhile will bid to close the gap on leaders Juventus later Sunday when they host Genoa.
Proceedings were cagey and pedestrian at first, but things soon livened up in the 21st minute when Inter's onslaught began.
Patrick Cutrone equalized for Milan by turning in a rebound of a shot from Lucas Biglia.
Portugal forward Andre Silva snatched the victor from close range with eight minutes left and there was still time for Franck Kessie to miss a last-minute Milan penalty, awarded for handball with the help of VAR.
Up next for the Rossoneri after the worldwide break: a visit to Juventus followed by the Milan derby.
Inter are now four points behind AS Roma whose third was consolidated by a 2-0 win at Crotone thanks to goals in either half from Stephan El Shaarawy and Radja Nainggolan.
A 2-1 victory at Torino for Fiorentina made it two wins in two matches for the Tuscan club since the sudden death of club captain Davide Astori.
It did not end there as Fiorentina were awarded a third penalty for handball, again with the help of VAR, which Cyril Thereau converted.
Jordan Veretout had scored Fiorentina's opener before a late equalizer from Andrea Belotti.
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