Ange Postecoglou admitted "wasteful" Tottenham lost their composure as Jamie Vardy's second-half equaliser gave Leicester a 1-1 draw against his profligate team on Monday.
Promoted Leicester survived a series of costly Tottenham misses either side of Pedro Porro's first-half opener for the visitors at the King Power Stadium.
Vardy made Tottenham pay for their erratic finishing with a typically predatory header, capping his surprise appearance just days after he had been ruled out by Steve Cooper after suffering a pre-season injury.
The 37-year-old has now scored nine Premier League goals in 17 appearances against Tottenham, who trudged off wondering how they had failed to demolish Leicester during their dominant first-half display.
Tottenham finished fifth in Postecoglou's first season following a campaign in which the Australian's commitment to all-out attack was eventually exposed at the cost of Champions League qualification.
Once again, Tottenham were hampered by poor finishing and unfocused defending.
Dominic Solanke was especially culpable on the striker's debut after moving from Bournemouth for a fee that could rise to GBP65 million ($84 million).
"Disappointing night for us. First half excellent and controlled the game but wasteful in front of goal. Once Leicester scored, the crowd lifted and we lost our composure," Postecoglou said.
"It was an issue we had last year as well. We need to keep working hard and be a bit more ruthless in front of goal. At times we made poor decisions.
"The dominance is great but if you don't score it is meaningless. We have to be stronger in our mindset in the front third. To be that wasteful is disappointing. We just weren't clinical."
Leicester are back in the Premier League after winning the Championship to end their one-year absence.
Amid reports the Foxes could face a points deductions for breaking financial rules, new boss Cooper needs to hit the ground running if they are to avoid relegation and this gritty display was an encouraging start.
"I was as fit as a fiddle until I got to about 65 minutes if I'm honest!" Vardy said.
"Tottenham are a really good team but we have them too much respect. We started getting after them and it changed the momentum.
"When we are at the top of our game we can give anyone a run for their money."
Tottenham went close to an early lead when Wilfred Ndidi cleared Rodrigo Bentancur's effort off the line before Mads Hermansen saved Brennan Johnson's fierce effort from the rebound.
Solanke's diving header was straight at Hermansen before Cristian Romero nodded Porro's cross just wide.
Solanke tested Hermansen with another header and Tottenham's pressure was rewarded in the 29th minute.
James Maddison floated a pin-point cross into the Leicester area, where Porro timed his run perfectly to flick his header into the far corner from 12 yards.
Maddison almost provided another assist moments later with a superb cross that Johnson fired narrowly wide.
Solanke should have done better than shoot straight at Hermansen early in the second half, while the over-worked keeper also saved Bentancur's close-range strike.
Tottenham's wastefulness came back to haunt them in the 57th minute as Leicester struck from their first effort on target.
Unhinged far too easily, Tottenham's defenders stood statuesque as Vardy was left unmarked in the six-yard box to head in Abdul Fatawu's cross.
It was exactly the kind of sloppy goal that bedevilled Tottenham during their swoon in the closing weeks of last season.
Vardy threatened to take advantage of more disjointed Tottenham defending, surging onto Bobby Decordova-Reid's pass but failing to find the accuracy required to beat Guglielmo Vicario.
Left prone on the pitch after an awkward collision, Bentancur needed treatment for seven minutes, including being given oxygen, before he was stretchered off to be monitored for a potential concussion.
Tottenham were shaken and Vicario had to plunge to his left to claw away Boubakary Soumare's header in stoppage time before Richarlison nodded wide from close range in a fitting end to the visitors' inconsistent evening.
