R2 is an absolute must when 1 on 1....
I'm not the best PES player lol but I never use R2, I find that its more about timing.
If you let it off at the moment the keeper starts coming off his line and you don't hit it straight at him, its guaranteed to go in. Basically as he's starting to come forward his ability to go sideways is greatly reduced but you have to time it so that you hit your shot before he gets close enough to actually smother it.