Jannik Sinner is yet to find his best form this Wimbledon, but has nevertheless reached the last four. Should his next opponent be discouraged or encouraged by this?

The answer will become clear when the defending champion plays his semi-final on Thursday (local time), against either Novak Djokovic or Felix Auger-Aliassime.

Then he will surely need to up his game having struggled to put away Jan-Lennard Struff, the world No.74 on Tuesday.

At 36, and in his 47th grand slam, Struff was the oldest man in the professional era to reach his first major quarter-final.

Sinner beat the German 7-5 7-6 (7-4) 6-3 but made 26 unforced errors and had to save a set point in the second set.

“A very, very tough player to play against,” said Sinner. “He deserves everything he has done and achieved in his career. Great person off the court.

“In the beginning I felt like he started better than me, I was struggling a bit. I tried to get into the match, I was serving a bit better, tried to stay there mentally, and of course very happy to be back in the semi-finals here.”

On another hot day in London there was no sign of a return of Sinner’s difficulty with the heat that caused his shock second round exit in Paris last month.

“We worked a lot, especially after Paris, trying to understand what went wrong there. It was a huge test today. I felt really comfortable on the physical side today so a big step forward.”

In the quarter-final suspended on Monday night by Wimbledon’s 11pm curfew second seed Alexander Zverev dropped the set in progress but still beat 13th seed Czech Jiri Lehecka.

Leading 6-4 7-5 3-3 overnight Zverev failed to win another game in the third set. The fourth went with serve until the tie-break, which the recent French Open winner took on his third match point, having double-faulted on his second.

Zverev, who will now play sixth-seed Taylor Fritz on Wednesday, said: “He (Lehecka) came out swinging but I’m happy to be through in four sets and not having to play another today.”