Zverev, who is ranked No.3 in the world – two places higher than Tsitsipas – fought back to defeat Jannik Sinner 5-7 6-3 7-6 (7-5) in his quarter-final match, denying his opponent another top-five seeded scalp after his prior win over Andrey Rublev.
"It means a lot, definitely, especially [with] how this year has been going so far for me," Zverev said after a gruelling three hours on court.
"I've lost long matches like that, so I’m happy I won this one."
Tsitsipas also orchestrated a superb turnaround against Diego Schwartzman, prevailing 6-2 6-7 (3-7) 6-4.
The Greek had looked set for a last-eight exit at four games down in the final set, only to stage a dramatic comeback to keep his hopes of a first title since last May's Lyon Open alive.
"There was a moment in the match where I felt what I was doing wasn't working," Tsitsipas said.
"He had a massive lead and momentum in what he was trying to do. I just tried to stay in the match as much as I could and that worked out very well.
"I wasn't expecting much at that point being a double break down, so I relaxed at that point."
Schwartzman meanwhile will rue his inability to put the tie to bed, having already reached two ATP finals this year.
Grigor Dimitrov and Alejandro Davidovich Fokina will face off in the other semi-final.
Bulgarian Dimitrov beat off Hubert Hurkacz in another final-set tie-break, winning 6-4 3-6 7-6 (7-2).
Fokina, who eliminated Novak Djokovic in the second round, turned over Indian Wells champion Taylor Fritz in another comeback result, triumphing 2-6 6-4 6-3.