In another late-night encounter on Rod Laver Arena, Olympic champion Zverev put Alcaraz to the sword in the first set two sets and survived a fightback to battle into the semi-finals with a 6-1 6-3 6-7 (2-7) 6-4 win on Thursday morning.
The 26-year-old admitted to feeling some butterflies when coming within a game of knocking off the world No.2 in the third set.
"When you're up 6-1 6-3 5-2, you start thinking. I mean we're all human," said Zverev.
"It's a great honour to play against guys like him and then when you're so close to winning, obviously your brain starts going and it's not always helpful.
"I fought back quite well in the fourth set, didn't let go and then very happy to finish the match."
Wimbledon champion Carlos Alcaraz had his fightback extinguished by Zverev in Melbourne. (Joel Carrett/AAP PHOTOS)
It marked the first victory of Zverev's career over a top-five player at grand slam level and equalled his best result at Melbourne Park.
The 2020 US Open runner-up will meet Russian world No.3 Daniil Medvedev on Friday for a place in Sunday's final at Melbourne Park.
The Spanish world No.2 swept past Zverev in straight sets at the same stage in last year's US Open, with the German looking ragged after spending almost five hours and 36 minutes longer on court than Alcaraz.
The on-court time discrepancy (five hours and five minutes) was similar leading in to Wednesday's quarter-final after Zverev survived two five-set epics through the first four rounds.
"I have a lot of blood under my toenails so that's quite painful," Zverev said when asked how his body was holding up.
"I take them out every single match but obviously when you run a lot they come back. So I just had to retape it.
"But, you know what, I would much rather feel the way I'm feeling right now with maybe a bit of pain here and there and be in the semi-finals than be at home right now watching this tournament."
Battered body aside, it was Zverev who raced out of the blocks to break the 20-year-old Spaniard twice in the first six games.
Down the other end, the German beanpole put on a dominant serving performance, winning almost 90 per cent of his first serves to claim the first set before Alcaraz barely had time to blink.
Alcaraz had to wait until 2-3 in the second set to bring up break point chances but could not convert either and was promptly broken twice to fall in to a two-set hole.
Not long after conceding another break, the usually powerful youngster slumped to his knees before throwing his racquet in apparent frustration.
Alcaraz finally broke Zverev as the German served for the match at 5-3, smiling to himself at the change of ends.
His smile got wider as the Spaniard won seven straight points in an inspired tiebreak to extend the match for a fourth set.
Feeling his bloodied toenails - and possibly also a momentum swing - Zverev called for the trainer before the pair traded breaks to open the fourth.
Zverev rediscovered his earlier form at 4-4 to break and didn't let his second chance to serve out the match go begging.
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