Second-seeded Zverev, chasing an elusive maiden grand slam title, was almost knocked down by, of all things, a feather before he steadied to prevail 7-6 (7-1) 7-6 (7-0) 2-6 6-1.
He will next face either world No.3 Carlos Alcaraz or 10-time champion Novak Djokovic, who play on Tuesday night, in his third Melbourne Park semi-final.
Zverev makes his feelings known after being ruffled by the feather. (Lukas Coch/AAP PHOTOS)
"To be honest, I should have been down two sets to love, he served (for) both of those sets. He played better than me," Zverev said.
"I was not playing great and I thought he was.
"I somehow won the first set, somehow won the second set, (then) I'm up two sets to love all of a sudden and I only need one more set.
"The fourth set was definitely the best that I've played and I'm obviously extremely happy to be back in the semi-finals."
Tennis' biggest unfulfilled talent, with two grand slam final losses to his name, Zverev won the first set in a tiebreak, fighting back after Paul served for the set at 6-5.
But with a serving Paul leading the second set 4-2, Zverev had his feathers ruffled - then almost imploded.
On break point, the German was incensed at the chair umpire after someone in the crowd yelled out just as he was about to swing at a ball close to the line - making him believe it had been called out.
No action was taken.
The 27-year-old then dropped the following point and received a code violation for an audible obscenity.
Then, at deuce, the umpire called a let after a feather landed near the ball just as Zverev was about to hit it.
It meant the point was replayed and Paul received another first serve.
Zverev plucked the feather - courtesy of one of the many seagulls in the Rod Laver Arena rafters - from the court and brandished it at the umpire in frustration.
"Buddy, it's a feather!" Zverev squawked.
"There's millions of them on the court."
Alexander Zverev was not happy after the umpire called a stop to this point due to a rogue feather landing on the court 🦅— Stan Sport (@StanSportAU) January 21, 2025↳ Australian Open 2025. Every Match. Ad-free. Centre Court in 4K, on Stan Sport.#StanSportAU #AO2025 #AusOpen pic.twitter.com/dQuQMUi3w7
But rather than implode, the German showed he was no featherweight, proving unflappable as he forced the set to a tiebreak.
Paul, 27, served for the set at 5-3 and earned a set point on Zverev's serve when leading 5-4, but couldn't take his chances and was broken.
The German demolished the American 12th seed 7-0 in the tiebreak.
But Paul again recovered, breaking Zverev early in the third set and teeing up three set points on serve at 5-2, and this time converting.
It proved only a brief setback for Zverev, who cruised through the fourth set to claim victory.
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