Things started to go sideways for Berrettini shortly after he lost a gruelling first set that lasted more than an hour.
He started the better of the two Italians, breaking serve twice in the first three games, and led 3-0 at the first change of ends. But Arnaldi, who had already logged the most hours on court en route to a major quarterfinal since 1991, got going after that, and won seven of the next nine games to steal the opening set.
A nine-deuce eighth game was a highlight, as Berrettini saved five break points to hold, but he could not repeat the feat in the set’s final game.
Berrettini later left the court for a medical timeout down 2-1 in the second set, but a love hold seemed to steady him briefly.
Though he bravely battled on for three more games, the former world No.6 had nothing left to give, and reluctantly pulled the plug after exactly two hours on court.