The Waratahs qualified for the Super Rugby plays off when they crushed the Brumbies 41-7 at ANZ Stadium in Sydney.
The bonus point result moves the Waratahs from seventh place into the top six but they will need to wait for the final match to find out who they will be playing next weekend.
The Waratahs showed their intent from the second minute when Lachie Turner scored the opening try which was converted by Kurtley Beale.
The Waratahs outscored Brumbies by five tries to one after the Brumbies scored a consolation try and first points after the full time siren.
Kurtley Beale created a first half try for Lachie Turner and kicked all seven of his kicks at the posts for a points tally of 16 and transformed the Waratahs backline when he moved from fullback to first five after Daniel Halangahu went off injured.
The Waratahs had scored two tries when Halangahu went off 10 minutes into the second half but with Beale directing the play they ran in three tries in the final stages.
The Waratahs led 10-0 after a close first half then ran away with tries after halftime from lock Sitaleki Timani, Dave Dennis and replacements Chris Alcock and Sosene Anesi.
The Waratahs' strength is their defence which has conceded only 20 tries in 16 matches this season and just six in home games.
The Brumbies scored a try in the second minute of injury time to avoid being held scoreless for the first time since 2005 and for only the second time in their history.
They also reduced what was the biggest winning margin for the Waratahs in matches against the Brumbies.
Wallabies flyhalf Matt Giteau created the try for winger Francis Fainifo and converted it from the sideline to end his 104-match Super rugby career.
Giteau is leaving the Brumbies to join French club Toulon from next season.
The Waratahs ensured they grasped their chance of a playoffs place with determination.
They had dropped out of the top six when they lost back-to-back matches in South Africa to the Sharks and Bulls but finished the regular season strongly, with wins over the Melbourne Rebels, Highlanders and Brumbies.
They dominated the first 15 minutes of Saturday's match but had only Turner's fourth-minute try to show for their superiority.
Beale made the try, squeezing between tacklers as the Waratahs attacked off turnover ball to give the final pass to his winger.
The elusive Beale was the Waratahs' best player throughout the first half, sounding out the Brumbies' defence, but New South Wales produced a more rounded attacking performance after halftime.
They built an overwhelming share of possession, established field position and minimized the errors that unpicked their attacking game before halftime.
"It was a really good second half," Waratahs captain Phil Waugh said.
"We had our chances in that first 15 minutes to score more points but didn't quite get over the line so to finish the way we did made it a really good night.
"Guys worked really hard...in games like this you have to work hard. "
"The guys, particularly in the forwards, worked hard tonight, won that contest and it was able to open up a bit more for the backs."
The Waratahs' 10th win of the season left only one playoffs place to be decided in a match later on Saturday between South Africa's Sharks and Bulls.
The Reds,y Crusaders and Blues qualified with wins in the last regular season round.
South Africa's Stormers have a playoffs place in hand ahead of their final match against the Cheetahs, leaving the Pretoria-based Bulls and Durban-based Sharks to contest the last available slot.
The Waratahs did not immediately know who their playoffs opponent would be or where the match would be played.
"It doesn't really bother us," Waugh said.
"We've worked to get where were are and now it's just a matter of getting out there next week."
After the tight first half, the second half on Saturday saw an avalanche of scoring with tries to Timani in the 47th minute, Alcock in the 60th, Anesi in the 67th and Dennis in the 75th.
Alcock's was the best of the game and one of the best of the season. He first wrestled the ball from Brumbies scrumhalf Patrick Phibbs near halfway and pushed off seven defenders in a 50 metre dash to the tryline.
The Brumbies ended their worst-ever season in terms of matches lost and look to the future under a new coach, former Springboks mentor Jake White.
"We were just outplayed," Giteau said.
"Credit to the Waratahs, their defence was really good and at the breakdown they really dominated us."
Final Score Waratahs 41 Brumbies 7
Tries - L Turner, S.Timani, C Alcock, S Anesi, D. Dennis
Pen - K Beale 2
Con - K Beale 5
Tries - F. Fainifo
Con - M Giteau
Referee: Craig Joubert
Assistant referees: Stuart Dickinson, James Leckie
Television match official: George Ayoub
Waratahs:15. Kurtley Beale , 14. Lachie Turner , 13. Ryan Cross , 12. Tom Carter , 11. Atieli Pakalani , 10. Daniel Halangahu , 9. Luke Burgess , 8. Dave Dennis , 7. Phil Waugh [c] , 6. Dean Mumm , 5. Sitaleki Timani , 4. Pat O'Connor , 3. Al Baxter , 2. Tatafu Polota-Nau , 1. Benn Robinson
Reserves 16. John Ulugia , 17. Jeremy Tilse , 18. Daniel Vickerman , 19. Chris Alcock , 20. Hugh Perrett , 21. Josh Holmes , 22. Sosene Anesi
Brumbies:1. Jerry Yanuyanutawa,2. Stephen Moore,3. Ben Alexander,4. Peter Kimlin,5. Ben Hand,6. Mitchell Chapman,7. Julian Salvi,8. Ita Vaea,9. Patrick Phibbs,10. Matt Giteau,11. Adam Ashley-Cooper,12. Pat McCabe,13. Tyrone Smith,14.Andrew Smith ,15. Christian Lealiifano
Replacements:16. Anthony Hegarty,17. Jono Owen,18. Henry Vanderglas,19. Tom Boidin,20. Josh Valentine,21.Francis Fainifo ,22. Robbie Coleman