Kiernan Dewsbury-Hall's first-half header was the difference as 22 Foxes players continued to build essential match fitness through the Club's summer programme of fixtures.
Backed by over 3,000 members of the Blue Army, it was a fresh-looking XI from new Manager Enzo Maresca. All three summer signings were in the line-up from the start - Conor Coady, Harry Winks and Callum Doyle. One familiar face in Foxes sides over the past decade was City's captain on the day as Jamie Vardy adorned the skipper's armband in Northampton.
Leicester were on top early on, although chances for either side were limited. One moment the sun shone, the next the fans were taking shelter from a sudden downpour. The first real Foxes opener didn't come until 20 minutes in when Doyle nodded Dewsbury-Hall's corner into Lee Burge's gloves. Later on, Wanya Marçal-Madivadua also had an effort blocked by Sam Sherring. The visitors' shape seemed to shift between phases of play, keeping Northampton guessing.
City's breakthrough came just before the half-hour mark. Ricardo Pereira, a scorer in Tuesday's behind-closed-doors defeat by Peterborough United, burst into the Cobblers penalty area, on the right side. His low cross was deflected away by Sherring. The ball, though, landed straight at the feet of Timothy Castagne, who crossed first time onto the head of Dewsbury-Hall. The Academy graduate's header was perfectly placed into the top corner. Smiles all round.
It could have been two for Maresca's men with seven minutes of the half to play. Louis Appéré's touch was loose and the ball fell at the feet of Marçal-Madivadua. The Foxes youngster sprung into action straight away, sliding a first-time through ball around the Northampton backline and into the path of a galloping Vardy. Leicester's No.9, though, hit his shot low and wide of the far post. Castagne slotted Vardy through again moments later but Sherring was able to deflect it behind.
Doyle, 19, made way at the break to be replaced by Victor Kristiansen. A valuable 45 in the tank for the Manchester City loanee. Daniel Iversen was on for the second half as well, replacing Jakub Stolarczyk. Unlike Tuesday's workout against Peterborough, Maresca wanted to give as many players as possible 60 minutes of playing time on this occasion.
Leicester went in pursuit of more goals in the second period. Only some heroics from the home 'keeper stopped them from making it 2-0 on 55 minutes. Dewsbury-Hall raced away down the left, cutting into the penalty area. Burge got fingertips to his cross, but the ball fell for Vardy. The Club's third all-time top goalscorer then forced an excellent stop from the Northampton No.1 before Dennis Praet hit it straight at the shot-stopper.
The hour was met with widespread changes for both teams. There were nine for the Foxes, with Wilfred Ndidi, Patson Daka and Kelechi Iheanacho among the players on for the final half an hour. Kasey McAteer was in the thick of it from the off, first seeing a drive blocked by a home trialist, before then crossing for Australia centre-back Harry Souttar to head over. A flowing move down the left channel ended with Iheanacho's low ball being diverted wide by Ndidi in the area. Daka also blazed over an inviting low drag-back by Ndidi from right to left across Burge's goal-line.
The Cobblers 'keeper had to be alert again with 10 to play. James Justin, making his second outing of the summer, hit a looping ball first time. It bounced up off the turf and required an acrobatic save to prevent it from bulging Burge's net. At the other end, another trialist for the Sky Bet League 1 hosts whipped a free-kick around the wall. Iversen did well to nudge it around the post, though.
Major moment - KDH's header
The game was settled by a solitary goal from Kiernan Dewsbury-Hall before the break, the result of the persistence of Ricardo Pereira, a pin-point cross from Timothy Castagne and a tidy headed finish from City's No.22.
Coming up - Preparations further afield
City can now look forward to exciting matches in Southeast Asia. Tottenham Hotspur are their opponents at the magnificent Rajamangala Stadium in Bangkok next Sunday (11am kick-off). Seven days later, on Sunday 30 July, the Foxes will be in Singapore to take on Liverpool at the National Stadium (10am kick-off) before returning to the UK at the end of the month. The Sky Bet Championship campaign, meanwhile, begins at home against Coventry City on Sunday 6 August (12pm kick-off). All times BST.