Hope you are doing great. I've been playing TEM for mac lately and I think there's a bug that someone reported in one of the earlier releases of TEM for PC.
It seems that if you lose the first set, 99% of the time you lose the second set also. You can be the best player in the world, with almost all the stats at 100% (including mental stats), but even if you play against a very bad player and lose the first set 7-6, you'll lose the second one by something like 6-0, 6-1 or 6-2.
And if you win the first set, you'll also win the second one easily, even against a much better player. I've played quite a few seasons in different save games and this seems to happen always.
Sorry if it has already been reported