Spurs boss Ange Postecoglou affirmed a few weeks ago that he "always" wins trophies in his second year in a job, and the Australian has taken a giant step towards ending Tottenham's 16-year drought, as Matheus Nunes's half-volley could not inspire a Citizens turnaround.
While Tottenham's smash-and-grab win over Coventry City in the third round was very much on the unconvincing side, Postecoglou's charges immediately took the game by the scruff of the neck against a lackadaisical Citizens side.
A sublime passing move out from the back allowed the hitherto profligate Werner to score his first goal of the season, and the hosts did not rest on their laurels after their surprise opener.
Spurs were aided by Man City being completely off the boil, and one became two in wonderful fashion as Sarr curled home a 30-yard stunner following a short corner routine, but that sweet strike finally seemed to wake the visitors up.
Tottenham's mission to get to half time with a two-goal lead ended in failure, as the increasingly influential Nunes pulled one back with a half-volley into the ground, no doubt changing the half-time team talks from both managers.
Spurs would also have to cope without Micky van de Ven for the second 45 - the Dutchman was in tears as he was forced off in the opening period - and as expected, the second 45 was one-way traffic.
The best chance of the second 45 fell to City youngster Nico O'Reilly, but Yves Bissouma produced an astonishing block to deny him, while Richarlison wasted a golden chance to make it three for the hosts after Josko Gvardiol's throw-in error.
However, Spurs showed serious steel to keep Guardiola's men at bay for the entirety of the second half, ensuring that there would be no 2024-25 quadruple for the Premier League champions.
TOTTENHAM VS. MAN CITY HIGHLIGHTS
Timo Werner goal vs. Man City (5th min, Tottenham 1-0 Man City)
What a move, what a finish!
Tottenham play it out from the back with unbridled confidence, as an exquisite backheel flick from Brennan Johnson sets Dejan Kulusevski away down the right-hand side.
The Swede picks out Werner on the opposite side, and the RB Leipzig loanee has all the time in the world to open up his body and curl a stunning first-time finish past Stefan Ortega. Is the redemption arc being written?
Pape Sarr goal vs. Man City (25th min, Tottenham 2-0 Man City)
In the script? Absolutely not! Spurs double their lead with an even better goal than Werner's quickfire opener.
This time, the German is involved in a short corner routine with Dejan Kulusevski, who tees up Sarr on the edge of the box, and the 22-year-old picks out the bottom corner with a perfectly-placed curling shot.
Could Stefan Ortega have done better at his near post? Maybe, but Sarr may never strike a cleaner ball for the rest of his career.
Matheus Nunes goal vs. Tottenham (45+3 min, Tottenham 2-1 Man City)
It had been coming.
Man City had been pushing to cut the deficit in half before the break and get their reward deep into added time, as Nunes's volley into the ground from Savinho's cross finds its way in.
MAN OF THE MATCH - DEJAN KULUSEVSKI
The creator of both of Spurs' goals on the evening, Kulusevski only had 30 touches of the ball at the Tottenham Hotspur Stadium, but a couple of his touches turned to gold.
The Scandinavian's pass to Werner could not have been any more perfectly-weighted, and he had the awareness to tee up Sarr for the pivotal strike, ending the night with four key passes in total.
TOTTENHAM VS. MAN CITY MATCH STATS
Possession: Tottenham 32%-68% Man City
Shots: Tottenham 11-15 Man City
Shots on target: Tottenham 7-3 Man City
Corners: Tottenham 4-4 Man City
Fouls: Tottenham 17-6 Man City