It depends on what do you mean by "direct". There is no elementary proof, as far as I known, even for polynomials when $d=2$, see page 8 of this [note](http://www.math.lsa.umich.edu/~hochster/balt.ps). When $d=1$, the statement is an easy exercise: one can write $f_1= da, f_2=db$ with $(a,b) = R$ since $R$ is an UFD. 

There are a few proofs of this very interesting theorem, analytic (the original one, over complex numbers), using duality theory ([Lipman-Sathaye][1], for all regular rings) and reduction to characteristic $p$ + tight closure (Hochster-Huneke, when $R$ contains a field, see the note in the first paragraph for some exposition of this method) but I am not sure any of them can be called direct. Any new proof will be very exciting!   

 [1]: https://projecteuclid.org/journals/michigan-mathematical-journal/volume-28/issue-2/Jacobian-ideals-and-a-theorem-of-Brianc-con-Skoda/10.1307/mmj/1029002510.full