Towards the end of the Second Age, Sauron was at the height of his power. Using his Ring, he had had centuries to build up an almost unchallenged dominion over most of Middle-Earth and had levied the entire human population of the south and east into his service.
Then, the army of Nùmenor led by King Ar-Pharazon landed near Umbar. Sauron marched his forces out to confront them… but was so outmatched that he didn't even bother to fight but instead surrendered on the spot.
There is absolutely no question of the much weakened Sauron of the Third Age being able to put up any sort of meaningful resistance to a full strength Nùmenor. Without the ability to take a fair form, he couldn't even try to repeat his plan B of 3000 years earlier - ingratiating himself with his foes, and subverting them from within.
