After a solid first jump, the 22-year-old Gu could not land cleanly the second time around. She skidded on her side, and one of her skis snapped off, sending her down to 17th place.
That put pressure on Gu to excel in her third jump, which she did. Instead of playing it safe, she chose a more complex trick and nailed it to temporarily move into first.
Meghan Oldham of Canada eclipsed Gu and ended the night top of the leaderboard. Mathilde Gremaud of Switzerland, the bronze medallist at Beijing 2022, was in third place.
In big air, skiers launch themselves off a jump and perform as many flips and twists as they can before landing. Judges assess height, technique, originality and other factors.
The combined tally of each skier's two best jumps determined which 12 of the 27 competitors advanced to Monday's final.
Two Italians, Flora Tabanelli and Maria Gasslitter, made it through to compete for a medal in their home country.