The defending Super rugby champions have still not found their best form this year but are growing in confidence the longer the season goes.
Michael Hooper, Adam Ashley-Cooper and Rob Horne all scored tries for the Waratahs on a wet and windy night in Sydney.
The Rebels were always behind but gave themselves a chance of snatching victory at the death when replacement Bryce Hegarty finished off a long-range try in the corner.
Jack Debreczeni, who had kicked three earlier penalties, landed the sideline conversion but time ran out for the visitors as the Waratahs held on over the final five minutes.
The win lifted the Waratahs into sixth place in the standings, in position for a playoff wildcard, but they can take top spot in the Australian conference if they beat the Brumbies next week.
The Waratahs recalled three forwards, Mitchell Chapman, Tatafu Polota-Nau and Jacques Potgieter and were rewarded with an early try to Hooper off the back of a rolling maul.
Ashley-Cooper crossed in the 20th minute to give NSW a 13-0 lead after Bernard Foley had booted an early penalty but Foley then missed some easy shots at goal.
The Rebels got on the scoreboard with a booming penalty from Debreczeni near the halfway line then cut the margin to four points with two more penalties after the break.
Horne scored out wide to restore the Waratahs' advantage before the Rebels launched one last raid which got them to within two. – Reuters
Original source: Waratahs scrape past Rebels