A towering header from new captain Wes Morgan and an emphatic strike from substitute Andy King ensured maximum points for Nigel Pearson’s men, who were thoroughly good value throughout an encouraging afternoon in the Leicestershire sunshine.
A touch frustrated by Peterborough’s admirable ability to retain possession in the first half, the Foxes still created the best of the chances before the interval.
And once Morgan, outstanding alongside young Liam Moore at the heart of the defence, powered home a Ben Marshall corner six minutes into the second period, Darren Ferguson’s visitors were never likely to recover. King’s thumping finish 15 minutes from time put the seal on a pleasing afternoon’s work.
A winning start was always going to be the most important thing to Pearson and his team, but there were so many more positives for the Foxes boss to take out of his side’s display.
Forced to be patient during a first half that saw the Posh interchanging fluidly and passing accurately, City were still sharp enough to look the bigger threat. And once they cranked up the tempo after half-time, they looked a real handful.
If they can carry that into Tuesday’s trip to Charlton, they’ll have every chance of making it two from two.
City have made starting well a habit in recent seasons – this was their fourth opening-day win in five seasons – but they were forced to bide their time in the first half. Peterborough, with a formation closely resembling Spain’s famous 4-6-0 at times, kept the ball with poise as they tried to draw the sting from their energetic hosts.
It took 37 minutes for either side to fashion a decent chance. The hard-working Jamie Vardy stole possession from Shaun Brisley inside the Posh half before his attempted centre for Beckford was turned towards his own goal by Gabriel Zakuani. Fortunately for the Posh skipper, goalkeeper Bobby Olejnik reacted smartly.
But it was the opening that seemed to spark the hosts into life. Two minutes later, a teasing cross from Marshall found the hanging Jermaine Beckford, who planted a 10-yard header a foot wide.
An incisive burst from the excellent Lloyd Dyer, whose cross went unconverted, closed out the half, but it was clear which side carried the greater threat.
Peterborough showed more attacking intent after the break and Kasper Schmeichel had to be on-guard on 49 minutes to block a firm drive from Paul Taylor.
But they fell behind two minutes later, albeit under slightly controversial circumstances.
Ferguson felt Morgan had fouled Zakuani as the two competed to meet Marshall’s right-wing delivery. He may have had a point.
But having let some similar challenges go in Zakuani’s favour earlier in the contest, there was some element of consistency in Craig Pawson’s decision to let this one go. Morgan made the most of it and headed in off the underside of the bar.
Suddenly Peterborough were right on the back foot. Beckford flung himself just shy of a Marshall cross, before his shot from a Paul Konchesky centre deflected just out of Vardy’s reach.
Vardy was denied by Olejnik again soon after and United substitute Emile Sinclair spooned over after stealing in from the right.
But City put the game beyond Ferguson’s men with 15 minutes to go through King’s remarkable ability to arrive in the right place at the right time.
The goal owed much to the tenacity of Vardy, who scurried away from Brisley down the left before showing the intelligence to pick out a telling pass. He found King arriving on the edge of the box and King speared a first-time shot into the top corner.
Sinclair’s pace continued to give Posh a glimmer of hope, but the United substitute struggled to trouble Schmeichel, who also saved smartly from Lee Tomlin near the end.
A winning start for the Foxes, who head to Charlton on Tuesday looking to keep their momentum going.
City (4-4-2): Schmeichel; De Laet, Morgan (c), Moore, Konchesky; Marshall, James (King 56), Drinkwater, Dyer (Knockaert 66); Beckford (Nugent 74), Vardy.
Unused subs: Danns, Logan, Waghorn, Schlupp.
Goals: Morgan 51, King 75
Booked: Marshall, De Laet
Peterborough (4-5-1): Olejnik; Alcock (Little 80), Brisley, Zakuani (c), Ntlhe; Frecklington (McCann 76), Newell (Sinclair 66), Boyd, Bostwick, Taylor; Tomlin.
Unused subs: Swanson, Day, Knight-Percival, Clarke-Harris.
Referee: Craig Pawson (South Yorkshire)