Spurs took the lead at the King Power Stadium in the 14th minute through a Rodrigo Bentancur goal but Nampalys Mendy and James Maddison scored in quick succession, while Kelechi Iheanacho netted on the stroke of half-time and Leicester went into the break with a 3-1 lead.
The north London side never really recovered after the first half and Harvey Barnes added a fourth to add more sheen to the scoreline for Leicester.
Son believes his side started well in the game but admitted that the game changed completely after Leicester scored twice within minutes.
The forward admitted that he is finding it hard to explain the loss as he felt that his team were at it but stressed that they need to learn their lesson from the defeat at Leicester.
Son was quoted as saying by the BBC: “We started quite well and created chances.
“After it was 1-1 we conceded a quick second goal and then it was open.
“It was a difficult game then. Leicester were so clinical, they almost scored every chance. It’s a very disappointing result.
“I think it’s very sad. We knew it was going to be a really hard game.
“In the Premier League, it’s never an easy game. It showed the Premier League has a high level.
“I don’t know what I can say, it’s very disappointing.
“I don’t think [it was complacency]. We came with a good feeling after beating City.
“The first minute we were really on it. We should be ready and learn something.
“Today should be a big lesson for us.”
Tottenham remain fifth in the Premier League table but they have played two games more than Brighton, who are four points behind them in sixth.
