After the ACT Brumbies had been upset by the Auckland Blues in Canberra, the Reds needed to score four tries and win to secure third place in the final standings and a playoff fixture back at their Lang Park home next weekend.
They duly delivered in an entertaining match against their oldest rivals with Scott Higginbotham, Liam Gill, James Slipper and Dom Shipperley grabbing the key scores before Will Genia added a flourish with a fifth try.
"We spoke all week about trusting the process rather than focusing on the result," skipper Genia said in a televised interview. "Things fell our way, I guess, but we worked hard all week for that result."
The result meant the Brumbies joined the Wellington Hurricanes in hoping the Bulls or Sharks would slip up in their final matches against the Lions and Cheetahs respectively in South Africa on Saturday evening.
Having been granted their chance, the Reds made it clear from the start they were not about to pass it up and number eight Higginbotham charged over the line from close range after three minutes.
The Waratahs have had a hugely disappointing season but the longstanding rivalry between the two states ensured they would not crumble and they gave as good as they got in the early exchanges.
With the Reds applying strong pressure near their line, however, prop Paddy Ryan paid the price for repeated infringements at the breakdown when he was yellow-carded in the 23rd minute.
The Reds took just a minute to take advantage with flanker Liam Gill going over the line under a pile of bodies but the Waratahs hit back almost immediately when winger Drew Mitchell got on the end of a grubber kick from flyhalf Bernard Foley.
Waratahs fullback Adam Ashley-Cooper then produced the completely unexpected with a towering drop goal from near the halfway line and the Reds went in leading 12-11 with neither the victory nor the bonus point assured.
Four minutes into the second half, however, and a third forward in prop Slipper breached the visitors' defence from close range before, in the 49th minute, Shipperley grabbed the fourth try after recovering a Mitchell fumble and racing 30 metres to the line.
Genia got his reward for another masterful performance with a typical scrumhalf's try when he sniped around the blindside in the 57th minute.
His halfback partner Quade Cooper was the second player yellow-carded for a high tackle on Berrick Barnes, who replaced the Queensland Red in the Australia team during the June internationals.
The Waratahs turned the screw and finally got their reward when replacement centre Tom Carter breached the home line to reduce the lead to 29-16 in the 73rd minute.
Reds centre Mike Harris, who converted two of the tries, scored his first penalty of the night with three minutes remaining to conclude the scoring and condemn the Waratahs to their eight successive defeat and 12th in 16 matches this year.
"It summed up our season," said Waratahs captain Benn Robinson. "There were patches where we played really good footie, but then we let teams in."