In first-round action, David Goffin produced two blistering sets to fight back and beat Stanislav Wawrinka 4-6 6-0 6-2 while Nick Kyrgios treated the crowd to an array of his antics in a 6-3 3-6 6-3 victory over Russian Daniil Medvedev.
Roared on by a partisan home crowd at the Foro Italico, Berrettini took the opening three games against Zverev, before the 2017 champion and last year's runner-up regained his composure.
Berrettini then saved five break points to take a 6-5 lead before the rattled Zverev, who beat the Italian in the same round last year, threw away the opening set with two unforced errors and a double fault.
Matteo Berrettini of Italy celebrates match point against Alexander Zverev of Germany in their second round match during day three of the International BNL d'Italia at Foro Italico on May 14, 2019 in Rome, Italy.
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They traded breaks early in the second before Zverev, who saved a match point in the 10th game, committed another flurry of errors, capped by a forehand into the net to hand Berrettini a memorable win.
Zverev has not gone past the quarter-final at any tournament since reaching the Acapulco final in early March.
The flamboyant and unpredictable Kyrgios again treated the fans to his best and worst as he combined spectacular shots with some poor behaviour.
The Australian won the opening point of the match with what is fast becoming a trademark underarm serve and breezed through the first set before cheers from the crowd turned to jeers amid a second-set meltdown.
Having dropped serve to hand Medvedev a 5-3 lead, Kyrgios blasted a ball over the stands, turned his back to Medvedev and exchanged words with the umpire before the Russian held to force a third set.
Nick Kyrgios of Australia plays a forehand against Daniil Medvedev of Russia in their first round match during day three of the International BNL d'Italia at Foro Italico on May 14, 2019 in Rome, Italy
Image credit: Getty Images
As if nothing had happened, Kyrgios got back to business as he hammered aces and winners, having also capped some good forays to the net with confident volleys to book a second-round clash with Norwegian Casper Ruud.
Goffin dropped the opening set against Wawrinka before he blew away the Swiss in the next two, the decisive moment coming in the second game of the third when the Belgian saved a double break point at 1-0 down.
He won the next five games and although Wawrinka briefly delayed the inevitable, Goffin was able to celebrate after his frustrated opponent blazed a forehand into the crowd.
In the women's draw, Kristina Mladenovic brushed aside French compatriot Caroline Garcia 6-1 6-2. The evening's standout encounter pits holder Elena Svitolina against Victoria Azaraneka.