Here's what I told my kids when I was teaching them tennis some years ago.
When you are the underdog, playing someone better or a better team, when you get a chance to win a set or the match, go for it. What I mean is at set or match point, think ace or winner, not rally. Better players can always dial it back to out-steady you, so if you play passively, you'll watch the few chances you have to win ... slip away.
Over and over again.
IMO you are better served going for it, two serves for an ace, that kind of thing. What I see often in my own circles is the lesser player ... (whom may well be 'lesser' because of the inability to win that handful of points that matter, to put the other guy away when they have the chance) ... get conservative just when they're up 5-1, or at set or match point. Then lament yet another loss, letting it slip away.
Be aggressive ... you have nothing to lose and even if you do go down, you'll go down fighting.