Both sides were guilty of giving away possession cheaply in the middle of the park and the match seemed destined for a goalless draw before Nyadombo found the back of the net in the second half.
The first chance of the match fell for the hosts in the 11th minute when Marc van Heerden’s corner was punched away by Arrows goalkeeper Nkosingiphile Gumede, but Donovan Thompson shot over the crossbar from the edge of the box.
The visitors then threatened in the 27th minute when Dillon Sheppard popped up on the right flank and unleashed a low drive which missed to the right.
Sheppard had an even better chance two minutes later when he received a through-pass from Elrio van Heerden on the left, but his powerful strike came off the crossbar.
Arrows almost committed a costly blunder in the 43rd minute when Thanduyise Khuboni and Gumede hesitated inside the box, allowing Ayanda Dlamini to gain possession before finding Dumisani Zwane at the far post, but his shot was saved by Gumede.
Collins Mbesuma had the last chance of the half when he connected with a cross from Thamsanqa Mkhize, but his glancing header went wide of goal.
In the second half Ayanda Dlamini saw his low shot saved by Gumede four minutes after the break, while Sheppard shot over the crossbar at the other end a minute later.
Arrows will count themselves unlucky as they came close to taking the lead with a brilliant free-kick from Sheppard in the 63rd minute, but yet again his effort came off the crossbar.
Substitute Katlego Mashego had another opportunity just outside the penalty area 10 minutes later, and his curled free-kick was brilliantly parried away by Tapuwa Kapini.
Usuthu took the lead in 78th minute when Bukasa Kasonga connected with a Van Heerden corner, but his header was blocked by Gumede, only for Nyadombo to head the ball into the back of the net at the far post.