Bonginkosi Ntuli netted the match-winner as AmaZulu boosted their survival prospects with a crucial 1-0 victory over league leaders Kaizer Chiefs at FNB Stadium on Saturday night.
It was an unexpected blow in Chiefs' ambitions to lift the PSL title this season.
The first half started at a slow tempo and the opening 30 minutes of play offered up very little in the way of goalmouth action.
AmaZulu started brightly, though, looking to hit Chiefs on the counter with their pace and the likes of Ntuli and Siyethemba Sithebe were causing all sorts of problems for the defence.
However, it was Chiefs who created the best chance of the first half as on 28 minutes, Leonardo Castro latched onto Lebogang Manyama's perfectly weighted through-pass before firing wide of the mark with just the keeper to beat.
And the hosts were made to rue that missed opportunity as Usuthu went on to claim the lead on the stroke of half-time. Talent Chawapiwa squared the ball into the path of Ntuli, who had the simple task of guiding the ball home at the back post.
Chiefs boss Ernst Middendorp opted to shake things up at half-time, bringing on Bernard Parker and Khama Billiat for Kearyn Baccus and Anthony Akumu.
The change did very little to alter the course of the game, however, as AmaZulu quickly stamped their mark on proceedings.
In fact, they should stretched further ahead in the 56th minute when Sphesihle Maduna burst into the danger area but with just the keeper to beat, he fired into the side netting.
The visitors again went close to doubling their advantage just two minutes later as Maduna launched forward on the break with two team-mates in support. However, the chance came to nothing as Maduna dallied on the ball for too long, allowing Daniel Akpeyi to jump in and smother the ball.
Amakhosi redoubled their efforts as the clock began to wind down and lodged their first noteworthy attempt on goal in the 72nd minute, but Billiat's tame header was easily collected by Siyabonga Mbatha in the Usuthu goal.
Billiat again threatened to level matters on 83 minutes but his attempted diving header flew narrowly wide of the target, and the substitute again failed to capitalise a few moments later with yet another header.
And, with time running out, AmaZulu almost notched a second goal as George Maluleka deflected the ball into his own crossbar as he attempted to cut out a square pass.
But that was the last chance of note as Usuthu held firm in injury time to claim a famous victory against the league leaders on their home turf.