A marathon first set
In the first boys' singles final between a Frenchman and a Belgian since 1953, the pair of 16-year-olds traded blows over a hotly contested 78-minute opening set.
It was Debru who drew first blood, breaking for 4-2, but Bailly, who had rallied from a set down in two of his three previous matches and saved three match points in the third round against top-seeded American Bruno Kuzuhara, pushed back.
The unseeded Belgian broke back immediately then levelled at four-all, before pushing Debru to a tiebreak.
To the delight of the French faithful, who spent much of the afternoon breaking into full-throated chants of 'GABRIEL, GABRIEL', it was Debru who held his nerve in the tiebreak.
He launched a perfect lob over Bailly's head to lead 5-3, and a few points later sealed the set with a smash winner, the ball kicking off the clay and sailing into the crowd as Debru celebrated with gusto.