They started like a house on fire in Wales with the ball being spun wide for William Small-Smith to crash over the line.
Ospreys responded with a penalty for Luke Price, soon cancelled out by Ruan Pienaar, but found themselves 10-8 up as Ma’afu Fia proved unstoppable from two metres out.
Price missed a penalty to extend the lead and defences remained on top for the rest of the half, and after the break the pendulum continued to swing – first the way of Cheetahs and then with Ospreys camped on the opposition line.
There was 42 minutes in total between scores but it eventually came the way of the visitors, with a catch-and-drive going ten metres for Arnoldi to touch down.
Cheetahs led 15-10, soon chipped back to 15-13 as Price nailed another penalty, but on 75 minutes Tian Schoeman got the all-important three-pointer to make it 18-13.
Ospreys fought for their lives and won a succession of penalties ten metres out from the opposition line, but after losing Sintu Manjezi to the bin they finally managed to win the ball fairly at a maul and celebrated wildly.
Junior Pokomela has long been one of the Cheetahs’ leaders on the pitch and it was the same story at the Gnoll on Saturday night, where he delivered a Man of the Match performance.
The openside was everywhere on the Welsh turf, claiming 40 metres off eight carries and winning several crucial turnovers to turn the tide.
Ospreys 13 - Try: Ma'afu Fia. Conversion: Luke Price. Penalties: Price (2).
Toyota Cheetahs 18 - Tries: William Small-Smith, Wilmar Arnoldi. Conversion: Tian Schoeman. Penalties: Ruan Pienaar, Schoeman.