The Waratahs won their fourth match in a row when they upset Super Rugby champions the Chiefs 17-33 in New Plymouth on Saturday.
The victory provisionally moves the Waratahs into second place overall - up from third - and they remain on top of the Australian Conference.
The loss for the Chiefs means they have suffered back to back losses and although they remain in 8th place overall they have missed a crucial opportunity to move back up the Super Rugby standings after last week's loss to the Hurricanes.
The Chiefs scored the first points of the match through a penalty but the Waratahs soon scored the opening try and held on to the lead for all but five minutes of the match.
The Waratahs outscored the Chiefs by three tries to two. Israel Folau scored the opening try for the Waratahs which took him to 11 for the season and a new Waratahs record for one season.
Waratahs captain Dave Dennis clinched the victory for the Waratahs in the 72nd minute after the Chiefs had rallied from 13-3 down at halftime to take a 17-16 lead with two second half tries to replacement Bundee Aki.
Flyhalf Bernard Foley added the gloss with a try on fulltime and maintained a perfect kicking record, finishing with three conversions and three penalties for a personal total of 20 points.
The win lifted the Waratahs to second place on the championships table, leaving them atop the Australian conference, while the Chiefs remained anchored in eighth place.
The Waratahs had lost their last eight games in New Zealand - a streak spanning four years - but turned that around on Saturday with a win which kept them strongly in contention for a home semifinal.
"It's been a couple of years since we had a win over here but we were really keen to put in a strong performance tonight," Waratahs captain Dave Dennis said.
"We're really pleased with the performance.
"They're a consistent team, we knew they'd keep fighting for the full 80 minutes and I thought we just stuck to our game well. Our discipline was probably a bit off there but we kept playing, attacking with ball in hand and we got some good tries there in the end."
The Chiefs had the first lead of the match at 3-0 with a penalty to returning All Blacks flyhalf Aaron Cruden but Foley tied the scores with his first penalty only seven minutes later.
The Waratahs had a try disallowed when winger Alofa Alofa combined with scrumhalf Nick Phipps on the blindside but the referees detected an earlier obstruction.
Folau's try in the 15th minute was also submitted to the scrutiny of the video referee before being confirmed.
The Wallabies fullback's 11th try of the season surpassed the Waratahs record previously held by winger Peter Hewat.
The Waratahs led 13-3 at halftime but the Chiefs rushed back into the match with tries to Aki in the 55th and 62nd minutes, both from kick chases.
On the first occasion, Cruden put the kick-through that Aki contested in-goal with teammate Tim Nanai Williams. On the second, the kick was provided by fullback Tom Marshall.
The Waratahs continued to hold the ball through a long sequence of phases and they were rewarded with Dennis's dashing try in the 72nd minute.
Foley then completed the rare cross-Tasman win by scoring and converting his own try on the fulltime siren.
The away win for the Waratahs puts them in a strong position for the play offs even though they have matches to come against the Brumbies and the Highlanders who are both in contention for the knock out stage.
The Waratahs finish their season against the Reds who they beat 32-5 earlier this season in Sydney.
The Chiefs have matches against the Highlanders, Hurricanes and the Blues in the run up to the play offs.
Final Score Chiefs 17 (3) Waratahs 33 (13)
Tries - B.Aki 2
Pen - A.Cruden
Con - A.Cruden 2
Tries - I.Folau, D.Dennis, B.Foley
Pen - B.Foley 3, K.Beale
Con - B.Foley 3
Referee: Chris Pollock
Assistant Ref 1: Richard Kelly
Assistant Ref 2: Grant Stuart
TMO: Ben Skeen
1. Jamie Mackintosh,2. Nathan Harris ,3. Ben Tameifuna ,4. Matt Symons ,5. Brodie Retallick ,6. Liam Messam ,7. Sam Cane ,8. Liam Squire ,9. Tawera Kerr-Barlow ,10. Aaron Cruden (c),11. Asaeli Tikoirotuma,12. Andrew Horrell ,13. Tim Nanai-Williams,14. Dwayne Sweeney ,15. Tom Marshall
Replacements : 16. Mahonri Schwalger ,17. Pauliasi Manu,18. Josh Hohneck ,19. Michael Fitzgerald ,20. Tanerau Latimer ,21. Brad Weber ,22. Gareth Anscombe,23. Bundee Aki
1. Benn Robinson , 2.Tatafu Polota Nau , 3.Paddy Ryan , 4. Jacques Potgieter , 5. Kane Douglas , 6. Dave Dennis (c), 7. Michael Hooper , 8. Wycliff Palu , 9. Nick Phipps , 10. Bernard Foley , 11. Rob Horne , 12. Kurtley Beale , 13. Adam Ashley-Cooper , 14. Alofa Alofa , 15. Israel Folau
Replacements : 16. Hugh Roach , 17. Jeremy Tilse , 18. Sekope Kepu , 19. Will Skelton , 20. Stephen Hoiles , 21. Brendan McKibbin , 22. Jono Lance , 23. Matt Carraro