The fortunes of these two pre-season promotion fancies were starkly contrasted as the Tigers ran riot at Sixfields.
Peter Taylor's side cemented their place at the top of Division Three after a brutal display of finishing but Richard Hill must surely have seen his chances of landing the permanent manager's job at Northampton disappear on the back of this rout.
Hill took charge for Tuesday's goalless draw at Lincoln after the sacking on Monday of Martin Wilkinson.
He was clearly unhappy after seeing his players cave in, and said: "I have thrown my hat into the ring but if I was made manager tomorrow I would change every one of them on that performance." Taylor could afford to be more upbeat, after goals from Stuart Elliott, Danny Allsopp, Jason Price, Ben Burgess and substitute Jamie Forrester, who put the icing on the cake with an injury-time goal against his former club.
Taylor said: "I always enjoy watching my team when they play like that and score goals. I know we are capable of doing that." Northampton were guilty of some shoddy errors in handing goals to City.
Skipper Paul Reid started the ball rolling by picking out Elliott in the 20th minute, allowing the Hull player to then advance and beat Lee Harper with a left-foot shot.
City's second came from top scorer Allsopp three minutes before the break when he sweetly timed a volley on the break and Price made it 3-0 midway through the second half after timing his run to the near post to perfection to meet an Allsopp cross.
It could have been worse for the Cobblers who conceded a penalty in the 70th minute and saw their goalkeeper Harper sent off by referee Martin Atkinson for the trip on Allsopp.
Substitute goalkeeper Glyn Thompson came off the bench to deflect the penalty by Burgess off the crossbar.
Paul Trollope briefly raised hopes of a ten-man revival nine minutes later when he volleyed home from the edge of the box but Burgess made it 4-1 in the 81st minute after Justin Whittle's header had crashed down off the underside of the crossbar.
The stage was then set for Forrester to score his first goal of the season on the ground where he spent two and a half years, the tiny striker slipping clear before curling a shot past Thompson.