Paris Olympics gold medallist Zheng Qinwen won the last seven games of the match to surge to a 1-6, 7-6 (7/3), 7-5 victory over Madison Keys on Saturday and reach the fourth round of the US Open.
After coming through the second-set tiebreaker, Zheng appeared to be out of steam in the final set.
The former world number four had to come through qualifying after a lengthy recovery from an elbow injury saw her ranking plummet.
Keys took charge with an early break and broke Zheng again for a 4-0 lead in a game the Chinese player led 40-0.
Keys held for 5-0 lead, but Zheng had a last stand in her. She saved match point at 5-1 and kept on rolling.
Keys, former Australian Open champion and runner-up at Flushing Meadows back in 2017, had taken the first set in just 23 minutes without facing a break point, dropping just five points on her own serve.
Zheng found her rhythm in a tight second set. A late exchange of breaks sent it to a tiebreaker, Zheng winning the last three points to force a deciding third set.
Zheng, currently ranked 121st in the world, will face either six-time Grand Slam champion Iga Swiatek or Czech Marie Bouzkova for a place in the quarter-finals.
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