Staying focused unless I'm extremely and obsessively interested in something has always been an issue for me. The easiest ways I've found to help deal with this is either to do some short meditation before matches (If you've never meditated before it may take a while to learn how to make it work for you) and also having some sort of sound whether it's a specific song that's a bit repetitive or just simple ticking like a clock, going on while you're playing to remind you to stay focused. For the latter it's better if you find 1 sound you like and only listen to when you're playing and want to be focused, so that way the association with hearing it and understanding what you should be doing is much more automatic.
I know that for you it's most likely an issue with your drive to play opposed to a general struggle with focusing, and I know these aren't perfect solutions but they help make it possible for me to play with some sort of competency. Anybody else with any other real advice would also be appreciated, because this is still a major issue for me and is probably the biggest thing holding me back from getting better at this game and achieving other goals I have in real life.