Courtesy of a straight-sets demolition job on former world No.1 and three-time AO finalist Daniil Medvedev, the 20-year-old Tien has become the youngest man since Nick Kyrgios in 2015 to reach the last eight at Melbourne Park.
His next opponent on Tuesday will be No.3 seed Zverev, the losing Open finalist in 2025 who is still chasing that elusive maiden major title.
Tien and the 29-year-old Zverev split their two meetings in 2025.
Tien won 6-4 6-4 in Acapulco, while the rangy German got his revenge in the opening round of the French Open, where he saluted 6-3 6-3 6-4.
"It's going to be a super tough match," said Tien.
"I was able to get him the first time we played, but the second time we played he beat me pretty bad.
"He plays great tennis here. He's the defending finalist, it's going to be a challenge, but I'm really looking forward to it."
Even at such an early stage in his career, Tien is putting together quite the record at Melbourne Park.
Last year on his Open debut, the Californian got through qualifying and then outlasted Medvedev in a gruelling five-setter in the second round before bowing out to Italian Lorenzo Sonego in the round of 16.
"I have a lot more experience now," said Tien.
"I have only had a year since then, but that's a lot more than I had then.
"So I think just the mental clarity in some of these moments, knowing how to handle matches like these a little bit better makes a really big difference."
Despite sitting in third spot on the world rankings, the 29-year-old Zverev is still searching for his first major title, with the big two of Carlos Alcaraz and Jannik Sinner divvying up the past eight between them.
He lost to Dominic Thiem in the 2020 US Open final, to Alcaraz in the 2024 French Open decider and to Sinner in last year's title match at Melbourne Park.
Either Alcaraz or home hope Alex de Minaur await the winner of the Zverev-Tien clash in the semis.
But Zverev knows he can't afford to look beyond his most immediate challenge.
"Learner is a great player," he said.
"He's very, very young, up and coming and I have massive respect for him. He's very under the radar, also.
"He's the same age as some other young guys and they are talked about more, but I think he's the one that performs best right now.
"I have huge respect for him and the work he's doing."
