After being taken to a decider against Miomir Kecmanovic in his opening match, Sinner has not dropped a set in his past four matches.
However, not all of those victories have been straightforward as the scoreline suggests, and the top seed has yet to find his best form at SW19.
That has yet to prove a major problem for the 24-year-old, who has upped his level when needed to claim the decisive breaks and get himself over the finish line.
But, with world number 48 Nuno Borges being the highest-ranked opponent he has faced so far, it remains to be seen how he will fare against someone like Djokovic or fourth seed Auger-Aliassime.
Against Struff, Sinner endured a slow start and was taken to deuce in three successive service games, while the 6ft 4in German cruised through his.
But Sinner clung on and remained composed to first break for a 6-5 lead before serving out the opener to take the lead.
After trading breaks in the second set, Struff had the chance to level the tie when he brought up a set point, but Sinner’s serve saw him out of trouble and he breezed through the tie-break.
The four-time major winner remained relaxed as he dropped just four points on serve in the third set and, after striking the decisive blow at 4-3, confidently served out the victory to seal his spot in the final four.
Sinner finished with 16 aces, won 84% of his first-serve points and offered up just two break points to Struff in a solid performance.
“I felt like I was serving quite intelligently today, even though I was up a break,” Sinner said.
“I tried to stay there mentally in every service game.”