Robson reached the final of the Junior Australian Open in January
Britain's Laura Robson suffered a shock defeat to Sandra Zaniewska in the French Open girls' singles second round, losing 7-6 (12-10) 1-6 6-3.
Robson, 15, the top seed, lost the first set in a marathon tie-break but responded strongly to level the match.
Zanuiewska, 17, has far more experience on clay and it showed as she raised her game again in the decider.
The Pole broke to lead 4-2 and, although Robson continued to battle, served out to clinch victory.
Robson, the reigning Wimbledon girls' champion, also reached the final of the Junior Australian Open in January and is top of the junior world rankings.
She had beaten Russia's Karina Pimkina 2-6 6-3 6-3 in the first round on Monday.
Fellow Briton Heather Watson, the 13th seed from Guernsey, lost 7-5 6-4 to France's Gracia Radovanovic in the first round on Monday.