Bellini skipped in near the right-hand touchline for his first try after 12 minutes before he quickly added a second when he got on the end of Giulio Bisegni’s chip ahead.
The 24-year-old Italy international then completed his treble with 15 minutes left, in what was a 37-14 victory for Zebre, when he was sent clear by centre Tommaso Castello.
The second top performer was flanker Callum Gibbins impressed for Glasgow Warriors against Ulster Rugby by scoring two tries to achieve 26 points.
Gibbins was put through under the posts after 21 minutes by Fraser Brown and he was driven over by his pack for his second, after half-time, although the Warriors eventually went down to a 36-15 defeat at the Kingspan Stadium.
Zebre have another star performer from the weekend in fly-half Carlo Canna, who kicked five conversions against the Ospreys to attain 22 points.
Canna played a big role in what was an impressive performance by his side, as they achieved six wins in a single Guinness PRO14 season for the first time.
Guinness PRO14 Final 2018 Ticket Information: Prices start at just €35 at www.ticketmaster.ie with tickets available to suit every experience.
To book hospitality visit: https://www.pro14rugby.org/hospitality
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