  A vortex lock-in transition was directly detected by torque magnetometry in
an overdoped YBa2Cu3O7 single crystal of low anisotropy (\approx 7). The
locked-in state was observed below the 3D to 2D crossover temperature Tcr = 76
K, independently of extrinsic pinning effects thanks to a high quality clean
crystal and the use of a vortex shaking technique. The shape of the torque
signal as a function of the angle between the applied magnetic field and the
crystallographic c-axis is in very good agreement with the model developped by
Feinberg and Ettouhami [Int. J. Mod. Phys. B 7, 2085 (1993)] for quasi-2D
superconductors, despite the low anisotropy of the material.
