The defending champion, ranked world number three, fought back for a 4-6, 7-6 (7/4), 6-2 victory to book her place in the quarter-finals and secure qualification for the WTA Finals in Saudi Arabia this November.
The 21-year-old American endured a challenging afternoon in Beijing, where play unfolded in front of a largely empty stadium split between shade and blazing sunshine. Bencic struck first, taking the opening set 6-4 as Gauff struggled to settle into rhythm.
The second set became a battle of nerves. At 6-6, Bencic held set point in the tiebreak, only to double-fault. The Swiss player's frustration boiled over, and she hurled her racquet after Gauff closed out the tiebreak 7-4 to level the contest.
With momentum shifting, Gauff capitalised by breaking early in the decider. Her consistency and speed around the court wore down Bencic, who faltered again on the final point, sending a return into the net to hand Gauff the match.
Gauff, who lifted the trophy here last year, will next face either Germany's Eva Lys or fellow American McCartney Kessler for a spot in the semi-finals.