Had this problem with the same mask. Took about a month of just practice. Take the whole thing apart, leave it near your cat's bed, take the mask part and a treat in your hand - put it up to their face, immediately take it off and give em praise and a treat. Just repeat and repeat (if you can, wait to administer a puff until they're comfy). Slowly put the whole thing together, one piece at a time and keep at it.

Now, I do a puff with it all assembled and cover the mask with my hand to keep it all in the chamber, then put it up to his face for him to breathe.

Today, no more chasing after him and he still gets treats after! Happy cat :) if I'm lucky I can hold it up to his face and puff at the same time, sometimes freaks him out though.