Zverev admitted after his win over Martin Klizan in the previous round that he had been struggling with a fever and it was evident in a performance littered with unforced errors.
Struff, who was 0-4 against his German compatriot before today, took full advantage to set-up a fourth-round showdown with 2016 finalist Milos Raonic.
In a sign of the dejected nature of Zverev’s performance, the 21-year-old won only five of his 20 second serve points and he was troubled by the power off Struff’s forehand wing all match.
The 28-year-old’s first foray into the Zverev serve came in the fourth game when he fashioned two break points, but that followed a nervy opening service game from Struff where he overcooked a pair of forehands and double-faulted.
He was grateful to avoid an early setback and his eyes must have lit up when Zverev began to show signs of fatigue midway through the opening set.
The German double-faulted as he attempted to serve out the game at 2-3 and he was guilty of being on his heels on break point when he arrowed a backhand long. At that point Struff was averaging a staggering 84mph on his forehand; Zverev’s, in contrast, stood at 66mph.
The 21-year-old did carve two break points out for himself as Struff served for the set soon after, but he was tentative in his approach to both points and the senior player on Stadium 1, to much duress, closed out the opener in 44 minutes.
Zverev conceded after his second round virtual bye two days prior to feeling “probably the worst I have felt going into a match” and his condition was scarcely going to improve as Struff raised his level to open the second set.
In fact, he was broken in his very first service game after staving off an initial break point and, in a microcosm of his afternoon’s performance, he contrived to completely miss the ball at deuce in the following game.
Struff was rolling with the momentum and his modest record against Top 10 opposition ensured he would not be relieving Zverev’s neck of his boot. He would break again for a 4-1 buffer and it was apparent only divine intervention would spare Zverev another round in the Californian desert.
Perhaps the only silver lining for the world number three is the avoidance of a rematch with his conqueror at the Australian Open earlier this year, Raonic, a match where Zverev lost his temper to the extent he patented a new form of racket destruction.
However, his flawless record against his compatriot went up in smoke as he served to restore pride at 5-1, broken dismally to love, no less.