Sabalenka's stunning clay-court form deserted her as she fell in straight sets, 6-4, 6-3, to Olympic gold medallist Zheng.
It was seventh time lucky for the world number eight as she at last got the better of her Belarusian opponent with a confident display under the lights in Rome.
After surviving early pressure on her own serve, Zheng broke Sabalenka to take a 3-2 lead in the first set before serving out.
Zheng then pounced in Sabalenka's first service game in the second frame to go up a break.
Sabalenka showed determination to make gritty holds in the fifth and seventh games of the set, but she could not make inroads on Zheng's service as the 22-year-old powered into the semis.
"It's been a long time that I haven't arrived in semi-finals," Zheng told Sky Sports after securing her first semi-final appearance of the season.
"It was not easy for me because at the beginning of the year, I had some struggles with my arm.
"So right now I'm just perfectly in shape and trying to play better tennis all the time."
Zheng will meet Coco Gauff in the last four after the American earlier beat Mirra Andreeva 6-4, 7-6(5).
Gauff has guaranteed herself number two in the women's world rankings with her solid displays in Rome, where she saw off seventh seed Andreeva.
Former US Open winner Gauff said that she had "a lot of confidence" for the last four, where she will face an opponent against whom she holds a 2-0 record.
Gauff, 21, is looking for her first title of the season ahead of Roland Garros, after losing the Madrid final to Sabalenka.