Yet to drop a set in just her third Paris campaign, the 18-year-old defied early nerves to avenge a defeat to her 2020 conqueror, 6-3, 6-1, and set a final showdown with world No.1 Iga Swiatek.
The Italian provided one of the most heart-warming stories of Roland-Garros two years ago when as a 139th-ranked qualifier she reached the quarter-finals before eventual champion Swiatek ended her breakout spell.
Trevisan denied Gauff in the second round of that run and added seeded victims Maria Sakkari and Kiki Bertens to her list.
The 28-year-old Florentine had rediscovered some of that form as she entered her first Grand Slam semi-final on a 10-match winning streak, following a maiden title in Rabat.
Gauff’s focus had narrowed since a first major quarter-final in Paris a year ago.
It never shifted beyond winning the next match rather than going all the way these days.
It had served her well through five previous rounds and did so again.