was a force play, became a tag play ?

[_Bruno_]

hi,
strange situation today.
R1,R2, 0 outs.
double steal and the batter hit a hig hflyball into leftfield.
R2, already behind 3rdbase thinks that the ball will be caught and runs back toward 2ndbase (to tag up) but the ball drops and the throw beats R2 to 3rdbase.

the offensive coach argues that R2 had already touched 3rdbase and he needs to be tagged out instead of just touching 3rdbase.

defensive coach says that he still has to run to 3rdbase and so its still a force play, despite the fact that R2 touched 3rdbase before.

whats the correct ruling ?
force play at 3rdbase oder is a tag at R2 necessary ?