Tiralongo finished ahead of David Arroyo (Caja Rural-Seguros RGA) and Fabio Duarte (Colombia) at the end of the 161.5km stage from Malè to Cles.
The Giro del Trentino was the third stage race victory for Porte this season (he also won Paris-Nice and the Volta a Catalunya) as he prepares for the Giro d'Italia, where he is expected to be the favourite for the overall victory.
He set up the Trentino victory with a sensational attack on Stage 2, where he established the final 22 second lead he would hold over Astana's Mikel Landa and Sky team-mate Leopold Konig.
Final general classification
1 Richie Porte (AUS) Sky 13hr 43min 41sec
2 Mikel Landa (ESP) Astana 0:00:22
3 Leopold Konig (CZE) Sky 0:00:58
4 Dario Cataldo (ITA) Astana 0:01:11
5 Damiano Cunego (ITA) Nippo-Vini Fantini 0:01:13
6 José Mendes (POR) Bora-Argon 18 0:01:15
7 Domenico Pozzovivo (ITA) AG2R 0:01:32
8 Louis Meintjes (RSA) MTN-Qhubeka 0:01:33
9 Romain Bardet (FRA) AG2R 0:01:34
10 Edoardo Zardini (ITA) Bardiani CSF 0:01:37