A champion in Wuhan in 2018 and 2019, Sabalenka improved her perfect record in the tournament to 16-0 and awaits Zheng Qinwen, who beat Wang Xinyu 6-3, 6-4 in the second semi-final later in the day.
Gauff, who was on a nine-match winning streak on the back of her title run in Beijing last week, played a perfect first set but committed a whopping 21 double-faults during a semi-final lasting two hours and 26 minutes.
Sabalenka has now won 19 of her last 20 matches, a stretch that includes titles in Cincinnati and at the US Open.
"The atmosphere was incredible," said Sabalenka, who was 2-4 down in the second set.
"It definitely felt like one of the biggest matches of my career because the crowd made it feel like it was a Grand Slam final."
Sabalenka struggled on serve early on and couldn't control her forehand as a clinical Gauff leapt to a double-break 5-0 lead inside 19 minutes.
The American dropped a mere two points behind her first serve and limited the Belarusian to just two winners throughout that opening frame.
If the first set was a rout, the second was a dogfight with six of the first eight games going against serve.
After 78 minutes of play, Sabalenka found herself in the lead for the first time in the match, inching ahead 5-4 to up the pressure on Gauff, whose serve abandoned her when she needed it most.
With Gauff's double-fault count rising, Sabalenka took full advantage and broke serve to level the contest and force a decider.
A marathon third game that witnessed seven deuces and three break points saw Sabalenka win a seventh consecutive game and hold for a 3-0 lead in the final set.
Despite Gauff's best retaliatory efforts to level for 4-4 Sabalenka held on to close out a gritty victory.