The result, Usuthu's first home win of the campaign, lifts the Durban outfit to seven points and joint-top of the table with SuperSport United, who boast a superior goal difference and will visit Mpumalanga Black Aces on Sunday.
The Dube Birds remain fifth in the standings with seven points from four games, two points behind the pace-setting duo following their first League loss of the season.
Ndulula, who scored the winner against his former side Orlando Pirates in their season opener, should have netted three minutes in but he fired wide from the middle of the box.
Edward Manqele, on loan at Swallows from Mamelodi Sundowns, was guilty of a similarly bad miss soon after at the other end, as he failed to hit the target in a one-on-one situation.
AmaZulu goalkeeper Tapuwa Kapini came to his side's rescue in the 18th minute, as he acrobatically denied Dikgang Mabalane after 'Terminator' was released by Bafana Bafana playmaker Lerato Chabangu.
Four minutes later Ndulula slotted the ball home in the area after being teed up by Nkosinathi Mthiyane.
Ndulula, his club's player of the month for August, had a great chance to get a second goal in the 38th minute but he put his effort wide after being put through on goal by Kulegani Madondo.
The Dube Birds threatened just before the break, but Kapini did well to scamper away Mabalane's cross, with Siyabonga Nomvethe lurking in the box.
The second half was desperately short of goal-mouth action, with neither side showing much promise on attack.
Man of the Match Kapini, however, had to be alert to tip over a dangerous Chabangu corner moments before the end to ensure his team the full share of the spoils.