The Augsburg team cannot be called mediocre. They have also won against strong teams like Bayern Munich.
But the match between Augsburg and Bayern Munich is not an ordinary game either. Augsburg is about an hour away and that is already a derby. Therefore such a game has a completely different atmosphere and the Undergog is playing differently than usual.
Well this and obviously Augsburg was also pretty lucky to have won that match against Bayern. Even though Bayern was maybe not as dominant as in the other 3 games before where they also did not win, they still had way more domination over the game and also way more chances to score than Augsburg. So in the end a victory of Bayern or maybe a draw would have been a fair result but definitely not a win for Augsburg.
So i also think that Augsburg will have a hard time to beat Schalke this sunday and i also think that they will probably fight against being relegated down to the second league until the end of the season. That is just my guess though.