The world number four underwent surgery on his right elbow in November and barely had any competitive court time leading into the tournament in Melbourne.
His doctor suggested that taking part in the first grand slam of 2022 was a remote prospect, but the Greek reached the last four on Wednesday after a 6-3 6-4 6-2 win over Jannik Sinner.
"I'm pretty sure my doctor is watching right now," the 23-year-old said in his on-court interview.
"We both didn't expect for me to be here, it was not part of our plan. He told me he didn't see me playing in Australia but I proved him wrong.
"He's a big tennis enthusiast and I am happy I found the right person to bring me back even stronger."
Tsitsipas outclassed Sinner on Rod Laver Arena to move into a second consecutive Australian Open semi-final and third in four years.
The Greek fourth seed broke early in each set on his way to a third win in four meetings with 11th seed Sinner, who was playing his second grand slam quarter-final.
Not even a brief rain delay that led to the roof being closed early in the second set could slow Tsitsipas, who delivered his best performance of the tournament so far.
"I am very, very happy with the way I served and used my tactics," he said. "Having the crowd support, it is truly unbelievable.
"It is part of the game. You never know what to expect from the weather. I knew I was heading towards the right direction.
"The conditions might have changed a little bit – slightly faster, not as bouncy – so my mind did. I tried to adapt and it just worked."
Tsitsipas will face either Daniil Medvedev or Felix Auger-Aliassime in the semi-finals.