Chile's Tabilo will play his first-ever last four match at a Masters 1000 event at the age of 26, after unfussily seeing off unseeded Zhang 6-3, 6-4 in one hour and 26 minutes on centre court at the Foro Italico.
Tabilo knocked out six-time Rome champion Novak Djokovic on Sunday and in the last four the 29th seed will face either world number five Alexander Zverev or Taylor Fritz who play the day's final match.
"It's just unbelievable, I just can't believe it right now, still trying to soak this in... Definitely an unforgettable two weeks for me," said a delighted Tabilo.
"It's definitely the best tennis of my life right now, but I mean, trying to keep a poker face there because inside I'm just so nervous, every time trying to close out the match gets a little bit tighter."
Tabilo, in fact, had far less trouble on Wednesday than he did in his battle with Karen Khachanov in the previous round, not facing a single break point on his way to the biggest match of his career at the last major tournament before the French Open.
Zverev, who won the Rome title in 2017, is the highest ranked man left in the event after Daniil Medvedev's elimination on Tuesday.
As well as Djokovic's exit, Italian world number two Jannik Sinner and third-ranked Carlos Alcaraz both dropped out injured before the tournament.
Holger Rune, who lost last year's final to Medvedev, Madrid champion Andrey Rublev -- ranked sixth in the world -- and beaten finalist Felix Auger-Aliassime have also been eliminated.
Sabalenka strolls
Women's second seed Sabalenka needed just an hour and 13 minutes to see off Jelena Ostapenko in straight sets, 6-2, 6-4 on her way to the semis, improving her record against her Latvian opponent to three wins and no defeats.
Crowd favourite Sabalenka will take on next the winner of two-time Australian Open champion Victoria Azarenka and Danielle Collins, this year's Miami Open winner, who face off later on centre court.
"With this amazing atmosphere and with this amazing support... that's why I'm super motivated here and that's why I always say that this is the dream tournament for me to win," said Sabalenka.
"I really enjoy playing here so I don't have to think about being focused... I'm just here enjoying it and doing everything I can to win every point I play no matter what the score. I guess that's the key."
The 26-year-old could get a rematch of the Madrid final which she lost in dramatic fashion to world number one Iga Swiatek earlier this month.
Sabalenka, who has won the two most recent Australian Opens, was in a different class to Ostapenko, a former French Open winner, who could do nothing in the face of some punishing hitting.
Rome is the first time since the 2013 French Open that the top three women have reached the last four of a WTA event of 250 level or higher, with Swiatek and world number three Coco Gauff in the other semi-final.
