The 27-year-old German was unable to find his peak level for much of a match played in the stifling afternoon heat on Rod Laver Arena but dominated his American opponent in tiebreaks to lock up the first two sets.
Paul bagged the third set but second seed Zverev upped his intensity to whip through the fourth.
“To be honest, I should have been down two sets to love, he played better than me. I was not playing great,” Zverev said after reaching his ninth Grand Slam semi-final, the most among active players who have not won a major.
“(Somehow) I’m up two sets to love and all of a sudden, I need only one more set, and the fourth set was definitely the best that I’ve played.
“I’m obviously extremely happy to be back in the semi-finals.”
Paul, semi-finalist in 2023, had beaten Zverev in their two previous meetings and worked assiduously to gain the upper hand in the first two sets only for the German to raise his game to drag him back into a dog fight.
“He did what he always does,” said the American. “He picks up his level at the big moments, and my level unfortunately dropped in the big moments today.”
Elsewhere, Paula Badosa advanced to her first Grand Slam semi-final at the third attempt after beating Coco Gauff on Tuesday but the Spaniard said that just reaching the final four did not give her license to play with more freedom.
“I’m never going to feel freedom until I win the tournament,” said the former world number two after her 7-5 6-4 win over an error-prone third seed Gauff.
“I’m always like this. It’s my personality, my character. Today, of course, maybe I had a little bit less expectations, but I still had pressure, because I wanted to win so badly.
“I’ll step on the court in the semi-finals, I don’t care against whom, and I’ll want to win so badly. That’s part of me. When I’m in the final round, my level rises and I just want to give my 100% there and leave it all on the court.”
World number 12 Badosa had fallen out of the top 50 due to a series of injuries, including a chronic back problem that made her consider retirement.