However, the 27-year-old played it down when asked if he is currently playing the best tennis of his life.

“You need to relax a bit,” he said after beating the 21-year-old Alcaraz. “Three fantastic matches, now the semi-finals will be very difficult. Taylor (Fritz) beat me a few times at the slams.

“Alcaraz has beaten me too many times this year, so I’m happy I got this one. We have a great rivalry and friendship, I’m always happy to play against him – unless he wins.”

Zverev continued his impressive form against Alcaraz, who suffered a chest problem during this tournament and once again wore a pink nose strip to aid his breathing.

“It was a difficult week for me because I was struggling with some physical problems,” said Alcaraz, who added that he hopes to return next week for the Davis Cup final in Malaga – which will also be teammate Rafael’s last professional tournament Nadal will be.

“Today, without a doubt, I faced one of the best players in the world, who played very solid and great tennis.”

Alcaraz still seemed to be feeling the effects of that illness and was again out of form, but showed some fighting spirit to save seven break points in the first set and then two set points – before Zverev converted the third superbly.

Zverev had saved four of those break points in the fourth game of the match, putting the point on Alcaraz’s serve when he was 6-5 up, but he hit a crosscourt forehand long after an extended rally. The Spaniard forced the tiebreak, but Zverev was able to get in front again.

After both produced brilliant shots during the tiebreak – including a great crosscourt lob from Alcaraz – Zverev did the best to ultimately secure the set.

His third set point saw the German dig out an attempted Alcaraz winner with a brilliant half-volley pick-up near the net. Alcaraz spooned the returning volley wide and Zverev roared with joy.

Zverev only needed to win that first set to secure his place in the last four, but he was determined to secure victory and take top spot in the John Newcombe Group.

The break in the second set was easier to achieve, when Alcaraz fired a direct volley into the net, giving away the immediate lead.

The third seed exerted enough effort to force two break points against Zverev at 3-2 – the first the German has faced in the entire tournament – ​​but could not convert before Zverev had completed the match.