I checked again, and actually, the mouse sensibility wasn't applied on game load, only when you changed it in the menus. I just updated the game to fix that, so you can re-dl it.
If it doesn't fix your problem, try to raise MouseSensibility under [Controller] in Tennis.ini (or the .ini of your profile if you had created one), then launch the game. Maximum value is 30.
You play in fullscreen, right ? If in windowed mode, then mouse sensibility should be handled by Windows.
== Mana Games ==
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