Zverev rails at Alcaraz timeout in 'one of the best battles ever'
The Spanish world number one fought through 6-4, 7-6 (7/5), 6-7 (3/7), 6-7 (4/7), 7-5 over a monumental 5hrs 27 mins in Melbourne to send the gutsy German third seed home.
There was controversy when Alcaraz pulled up in pain clutching his right thigh at 4-4 in the third set.
He was allowed to have treatment at the changeover, leaving Zverev furious and angrily remonstrating with officials.
Medical timeouts are not permitted solely for muscle cramping.
"He was cramping, so normally you can't take a medical timeout for cramping," said Zverev.
"What can I do? It's not my decision. I didn't like it, but it's not my decision."
Asked what he told the officials on court, he replied: "I just said it was bullshit, basically.
"To be honest, I don't want to talk about this right now," he added. "Because I think this is one of the best battles there ever was in Australia.
"It doesn't deserve to be the topic now."
Defeat was another bitter pill for Zverev, who is still searching for a first Slam crown aged 28 after being a three-time finalist, including last year in Australia when Jannik Sinner beat him.
He said he simply ran out of gas.
"Unfortunate ending for me, but to be honest I had absolutely nothing left in me," he said.
"Even at 5-4 (leading in the fifth set), you know normally I can rely on my serve a bit more. My legs stopped pushing upward, that's the way it is. This is life. We move on."
Asked if he had any regrets, he pointed to not winning the second set.
"That one, for me, I felt like I should have won, especially serving for it. I didn't play a good game serving for it," he said.
"Funnily enough, I don't have many regrets in the fifth set because I was hanging on for dear life, to be honest. I was exhausted."