<p>The match lasted five hours and 26 minutes and ended with both men moving as if badly blistered.</p><p><strong>"I don't know how I am standing here," </strong>said Arnaldi, adding that he had been hobbled by a foot injury earlier in the year.</p><p>It was his second consecutive five-hour match after his five-set win over Raphael Collignon in the previous round.</p><p><strong>"In the third set I was so tired,"</strong> he said.</p><p>Tiafoe appeared to be cruising when he raced 4-1 ahead with a double-break in the fourth set, flat-footing Arnaldi with quick hands and unexpected angles.</p><p>Instead, with the Americans' own footwork slowing, Arnaldi won nine of the next 13 games, as well as a tie-break, to move 4-2 ahead in the fifth.</p><p>Yet the 28-year-old Tiafoe hauled himself to 4-4.</p><p>Arnaldi seized back the initiative by breaking the love.</p><p>The Italian wasted a first match point with a double-fault, but, despite some brave hitting by Tiafoe, finally took his third chance.</p><p><strong>"At some point, it wasn't tennis, it was something else," </strong>Arnaldi said. <strong>"You were just playing with everything you had. There had to be a winner, and fortunately, it was me."</strong></p><p>Arnaldi will face another unseeded Italian, resurgent Matteo Berrettini, in the quarter-finals.</p><p>Flavio Cobolli, the top Italian seed at 10 following the early elimination of world No.1 Jannik Sinner, will play fourth-seeded Felix Auger-Aliassime in the last eight.</p>