Reigning champions United hammered Bolton 5-0 at the Reebok Stadium thanks to a hat-trick from Wayne Rooney and a double from Javier Hernandez as Sergio Aguero also pulled out a treble of goals in City's 3-0 home win over Wigan Athletic.
The results have the Mancunian clubs sitting two points clear of third-placed Chelsea at the top of the table with United shading City by three on goal difference.
The 18 goals scored by United in their opening four matches is a club record whilst City's 15 is nothing to sneeze at, especially as Roberto Mancini was able to rest Edin Dzeko who netted four times the last time he played.
Elsewhere in England's top flight, Arsenal were able to record their first win of the season with a lucky 1-0 result at home to Swansea City thanks to Andrey Arshavin's opportunistic 40th minute goal following Michel Vorm's goalkeeping error.
Aston Villa twice came from behind to hold Everton 2-2 at Goodison Park with Stiliyan Petrov and Gabby Agbonlahor on target for the visitors as Leon Osman and Leighton Baines (penalty) provided the goals for the Toffees.
Everton's Merseyside rivals Liverpool were desperately unlucky to lose 1-0 at Stoke City (Jonathan Walters penalty) with some questionable refereeing decisions hindering the match as Chelsea put in their best performance of the season with a 2-1 away win at Sunderland - John Terry and Daniel Sturridge's goals doing the damage as Ji Dong-won grabbed a late consolation.
Tomorrow sees Norwich City host West Bromwich Albion at Carrow Road prior to Fulham's home clash with Blackburn Rovers and then QPR are at home to Newcastle United on Monday night to complete the fourth week of Premier League play.