Matteo Berrettini upset Alexander Zverev 7-5, 7-5 in second-round action in Rome.
Berrettini, a 23-year-old wild-card entrant who is ranked 33rd in the world, moved into the Round of 16 in an ATP Masters 1000 event for the first time in his career.
The Italian 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.
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 that handed Berrettini a memorable win.
The result is the latest in a line of success for Berrettini. He captured his second career ATP Tour title on April 28 at Budapest, Hungary, then reached the final at Munich on May 5 before losing to Chile's Christian Garin in a third-set tiebreaker.
As for Zverev, he has advanced past the quarterfinals of just one tournament this year, making the final at Acapulco, Mexico, in early March.
Zverev said of the Tuesday result, "Environment was great. The match that I played was horrendous."
