I have said this a few times on this forum but I call it leaking mental juice!!! Getting into a comfort zone after going up and thinking, "what the heck, I'm a few up I can loose this hole" is the worst attitude... Put your foot on his throat and do not let it off until he is closed out!!! You want to win a 9 hole match 5/4 and you want to win a 18 hole match 10/9. Until you get there do not feel like you have won, YOU HAVE NOT WON CRAP!
I'm sure everyone is different, but for me, I don't focus on the match all that much. Sure, there are times when you have to, like playing smarter, maybe laying up if you have a nice lead, making a putt to put the pressure on your opponent. But normally I just play against the course, and let the rest take care of itself.
If you're finding fairways, getting on in regulation, and not using a ton of putts, you're going to win your match.