Zhao had established control of the semi-final by winning all eight frames in a remarkable session on Friday morning and he returned to finish the job in emphatic style later in the day.
Trailing 12-4 advantage in the evening session, O’Sullivan was unable to force a momentum shift.
Zhao’s aggressive break-building piled the pressure on O’Sullivan and there was no stopping him becoming the second Chinese player to reach the World Championship final after Ding Junhui, who lost to Mark Selby in 2016.
The 28-year-old left-hander, bidding to become the first Chinese world champion, will face Judd Trump or Mark Williams in the final, which runs from Sunday to Monday.
Zhao applauded his hero O’Sullivan after they warmly shook hands at the end of the match.
“I can’t believe that. I need to say thank you to Ronnie because he has helped me a lot before. He’s my idol,” Zhao said.
“I’ve just tried to enjoy the Crucible. It’s an amazing time for me and I just want to enjoy it because I don’t know how many times it can happen here.
“I’ve played here and sometimes the crowd is helpful for Ronnie and he deserves that. He is a legend here so I needed to control myself.”
Asked how he will celebrate the memorable victory, Zhao said he planned to have a “big lunch.”
“Zhao played good, he deserved his victory. I think he’s done brilliantly all tournament and all credit to Zhao,” O’Sullivan said.
“I’ve been awful for quite a while, those performances are in there, they’ve been coming out quite regularly recently.
“I just felt like I never gave him a game so that’s a bit disappointing.”
Seven-time champion O’Sullivan had the tip on his cue changed overnight, having labelled it as “awful” ahead of the last-four clash at Sheffield’s Crucible Theatre.
But the Englishman lost all eight frames on Friday morning as Zhao ruthlessly punished every missed pot and poor safety to inflict only the fourth session whitewash of O’Sullivan’s long World Championship career.
Former UK Championship winner Zhao is playing as an amateur in Sheffield as he continues his comeback following a 20-month ban for his involvement in a betting scandal.
In the other semi-final, Williams fought back from a four-frame deficit against Trump to level at 8-8.
Trump resumed 5-3 ahead from Thursday’s session and looked like maintaining control after winning the first two frames of the day.
But Williams replied with breaks of 105 and 84 before edging a scrappier 13th frame to trail 7-6.
Trump took the next frame but Williams shaded a tense 15th, sealing it on the last pink.
A superb 96 clearance from the Welshman ensured parity going into Saturday morning’s session. (AFP)
