Sergio Aguero and Jesus Navas both struck twice as City, who have scored 13 goals in their last two home games, roared into the top four. Hapless Tottenham conceded as many in one match as they had in their previous 11 league outings.
A sixth home win in six gave Manuel Pellegrini's team 22 points from 12 games. United were poised to move above them when they led Cardiff in south Wales with goals from Wayne Rooney and Patrice Evra.
The visitors were then denied a fourth consecutive league victory when Kim bo-Kyung's late header earned Cardiff a deserved share of the spoils and left United in sixth spot with 21 points, seven behind leaders Arsenal.
England striker Rooney was at the centre of controversy when he escaped with a yellow card for a wild kick at Jordan Mutch but the performance of a goal-laden weekend came from Manchester City.
Oddly enough Tottenham enjoyed territorial superiority but having fallen behind after 15 seconds they were ripped apart by a home side bursting with goalscoring potential.
City have scored 34 league goals already this season and manager Pellegrini was glowing in his praise.
"It's not normal to win by six goals against a strong team like Tottenham. I think today we played really well, not just attacking but defending," he told Sky Sports television.
"Spurs have very important players in attack so to not concede is very good."
City were gifted the lead straight from the kickoff when Tottenham played the ball back to Hugo Lloris and the France keeper hit his clearance straight to Aguero.
Lloris, playing for Spurs for the time since suffering concussion against Everton at the start of the month, parried the Argentine striker's effort but the ball rolled to Navas whose chip curled over the out-of-position keeper.
It was the second fastest goal of the season after the wind-assisted one scored by Stoke City goalkeeper Asmir Begovic against Southampton in 13 seconds.
Tottenham's afternoon got steadily worse as they slumped to their heaviest league defeat since a 7-1 mauling at Newcastle United in 1996.
"It was a difficult start for us after that. Everything you had in mind goes down the drain," said Tottenham's stunned manager Andre Villas-Boas, in charge for the 50th league game.
"Everything went bad for us from being one of the best defences in the country to suffering six goals. There's not a lot we can say. City were excellent, we were extremely poor today and paid a heavy price."
Another poor clearance by Lloris led to the second goal after 34 minutes when Younes Kaboul's clearance from Aguero's shot cannoned in off Tottenham midfielder Sandro.
Aguero's deft finish just before halftime effectively killed off Spurs and when he and Alvaro Negredo produced superb finishes early in the second half the Londoners were in danger of suffering their worst Premier League defeat.
Villas-Boas gave striker Emmanuel Adebayor his first appearance of the season after the break but Tottenham's goal-shy attack rarely threatened City goalkeeper Costel Pantilimon, again selected in place of England's Joe Hart.
Navas ran through to complete the rout in stoppage-time after a defence-splitting 50-metre ball from James Milner.
While City appear to be on the up despite some poor away results, Tottenham, who have managed a meagre nine goals in 12 league games, have slipped to ninth with 20 points.
After their worst start to a Premier League season, David Moyes's United have begun to climb the table and looked to continue their improvement at Cardiff.
Rooney, who was lucky to stay on the pitch after tangling with Mutch early on, fired them ahead after 15 minutes following a sharp turn.
Cardiff equalised through former United striker Fraizer Campbell after a flowing move and were matching the champions all over the pitch until Evra headed in Rooney's corner on the stroke of halftime.
In a thrilling finale Kim headed Cardiff level in stoppage time only for Rooney to then waste a glorious chance to snatch victory for United at the other end.
"It was disappointing not to take all three points," said Moyes.
Despite television evidence to the contrary he and Cardiff counterpart Malky Mackay agreed Rooney did not deserve to be sent off.
"That was not a lash out in any way," said Moyes. "It was about feeling hard done by with the boy running across his path."