The result kept the Waratahs at the top of the Australian conference while the Chiefs hopes of defending their crown for a third time were in tatters as they suffered their fifth loss and slipped well outside the crucial top six.
After trailing for much of the game, the Chiefs seized a 17-16 lead with two snappy tries midway through the second half before the Waratahs reasserted their dominance to record their first win in New Zealand for four years.
"We were really keen to put in a strong
performance and are really pleased with the result.
"We kept playing,
kept attacking with the ball in hand and got some good tries in the
end," Dennis said.
After their hiding at the hands of the Hurricanes a week ago, the Chiefs rejigged their backline with the return of Aaron Cruden to the driving seat and Andrew Horrell and Tim Nanai-Williams stationed outside.
But the defensive lapses from a week ago remained as Adam Ashley-Cooper ripped apart the midfield.
A rueful Chiefs coach Dave Rennie admitted at half-time his side were "lucky" to only trail by 10 points such was their inability to contain the Sydneysiders.
After the Waratahs were denied an Alofa Alofa try when the television match official detected interference at the start of the move, Ashley-Cooper engineered the first five-pointer when he beat three to send Israel Folau over.
A conversion and three penalties by Bernard Foley to a penalty by Cruden put the Waratahs ahead 13-3 at half-time.
The Chiefs made a better showing at the start of the second half but a kickable penalty attempt by Cruden hit the posts and the option to take a lineout over a close-range penalty was snuffed out by a misdirected throw.
Their breakthrough came in dubious circumstances when Bundee Aki scored the first of his two tries following up a Cruden chip kick with question marks over whether he was on side at the start of his run and whether he forced the ball legitimately.
But there was no doubting his second try, following the same formula with Aki sneaking behind the Waratahs defence, and with All Blacks pivot Cruden converting both tries.
However, there was no holding back the Waratahs over the closing stages as Dennis scored when Folau ignited a counter-attack after a Chiefs clearing kick failed to find touch, and Foley scored their third try to cement the outcome.
Foley finished with a match haul of 20 points from his try, three conversions and three penalties.
Scorers:Chiefs: 17 - Tries: Bundee Aki (2); Conversions: Aaron Cruden (2); Penalties: Cruden
Waratahs: 33 - Tries: Israel Folau, Dave Dennis, Bernard Foley; Conversions: Bernard Foley (3); Penalties: Foley (3), Kurtley Beale
Teams:
Chiefs
15 Tom Marshall, 14 Dwayne Sweeney, 13 Tim Nanai-Williams, 12 Andrew Horrell, 11 Asaeli Tikoirotuma, 10 Aaron Cruden (c), 9 Tawera Kerr-Barlow, 8 Liam Squire, 7 Sam Cane, 6 Liam Messam, 5 Brodie Retallick, 4 Matt Symons, 3 Ben Tameifuna, 2 Nathan Harris, 1 Jamie Mackintosh
Substitutes: 16 Mahonri Schwalger, 17 Pauliasi Manu, 18 Josh Hohneck, 19 Mike Fitzgerald, 20 Tanerau Latimer, 21 Brad Weber, 22 Gareth Anscombe, 23 Bundee Aki
Waratahs
15 Israel Folau, 14 Alofa Alofa, 13 Adam Ashley-Cooper, 12 Kurtley Beale, 11 Rob Horne, 10 Bernard Foley, 9 Nick Phipps, 8 Wycliff Palu, 7 Michael Hooper, 6 Dave Dennis (captain), 5 Kane Douglas, 4 Jacques Potgieter, 3 Paddy Ryan, 2 Tatafu Polota Nau, 1 Benn Robinson
Substitutes: 16 Hugh Roach, 17 Jeremy Tilse, 18 Sekope Kepu , 19 Will Skelton, 20 Stephen Hoiles, 21 Brendan McKibbin, 22 Jono Lance, 23 Matt Carraro