As far as I know, NCE (Noise Contrast Estimation) is different from sampled softmax from tensorflow, see Jozefowicz et al. (2016) or here 70 for a comparison.
EDIT: sorry, I see that original link is to a page with a number of different softmax approximations, and NCE is one of them. I personally would be more interested in sampled softmax, as it tends to work better for me.
EDIT2: here 74 is a TF implementation of sampled softmax and NCE, hopefully they can be implemented using existing pytorch functions.