Anver Esterhuizen scored the only goal of the game four minutes from time, heading home Tsietsi Mkhwanazi's cross.
The hosts were the better side in the first half, with Dumisani Zwane on target in the 17th minute, but his effort lacked the power to trouble Tshepo Motsoeneng.
Roger Palmgren's men spent a lot of time in Stars’ half, but failed to get behind the defence and were forced into taking shots from a distance.
Ten minutes later the ball fell for Carlington Nyadombo just outside the area, but he also failed to hit the target as his powerful strike went wide of the left post.
The second half saw Stars committing more men forward and they almost went ahead in the 46th minute, only for Dove Wome to lift his strike over the crossbar.
Lehlohonolo Thebakang had an even better effort five minutes later as he managed to beat goalkeeper Philani Zikalala from the left, but his shot came back off the upright.
The hosts then threatened at the other end, but failed to make it count as subsitute Josef Lekata was unable to reach a low cross from Ayanda Dlamini with less than ten minutes to play.
The visitors took advantage of that missed chance in the 86th minute when Esterhuizen ran ahead of his marker to head a cross from Mkhwanazi into the back of the net.
Usuthu had one last chance to grab a point in the 90th minute from a set-piece, but Marc Van Heerden saw his curled effort dipping just wide of the post.