The South Korea striker responded to Antonio Conte’s decision to drop him to the bench after a barren start to the season by coming on to curl home two fantastic strikes and slot home a late third.
Spurs trailed to Youri Tielemans’ early penalty but took advantage of the Foxes’ failings at set-pieces as Harry Kane and Eric Dier nodded home from corners to turn the game around.
James Maddison’s fabulous first-time finish briefly drew Leicester level again, but Wilfried Ndidi’s mistake allowed Rodrigo Bentancur to steer Tottenham back in front before substitute Son stole the show.
Victory maintained Spurs’ unbeaten start to the Premier League season as they climbed to second, level on points with leaders Manchester City.
Leicester, meanwhile, remain at the foot of the table, still searching for their first win, despite having led in four of their seven matches thus far.
As at all Premier League games this weekend, fans observed a minute’s silence for the late Her Majesty Queen Elizabeth II and a 70th-minute round of applause in honour of her 70-year reign.
Son shines as Conte call proved right
In fairness, he could not have asked for better opposition to open his account, given the brittleness of the Foxes’ backline but the quality of his first two strikes stood out.
Both were curled into the top corner from the edge of the box – the first with his right foot, the second with his left – as the 30-year-old proved the old adage that form is temporary but class permanent.
Even an erroneous offside flag could not deny him the match ball as VAR replays showed he was just onside when he strode clear to beat Danny Ward for his third goal and Spurs’ sixth.
Five different players provided assists, with Ivan Perisic’s dead-ball delivery complementing Dejan Kulusevski’s crosses from open play, while Bentancur contributed his first goal for the club.
But they will need to cut out defensive lapses such as Davinson Sanchez’s needless challenge on James Justin that handed Leicester their early lead, Tielemans tucking home at the second attempt after VAR spotted Hugo Lloris had encroached off his line in saving the initial spot-kick.
Foxes’ fiascos hitting new lows?
When it comes to defensive debacles, however, no top-flight team is a patch on Leicester, who have now lost 4-2, 5-2 and 6-2 on the road this season, conceding a joint-high 19 goals overall.
It is not a new phenomenon either – they have kept just two clean sheets in 19 games, conceded 25 set-piece goals since the start of last season and dropped 11 points from winning positions this term alone.
While boss Brendan Rodgers, enduring the longest losing league run of his career after six successive defeats, said earlier this week the club’s hierarchy had been “very supportive”, that patience surely has a limit after a haul of just one point from seven games.
The dithering Ndidi’s error to help Bentancur put Spurs 3-2 up at a vital juncture of the game characterised their lack of confidence, while deadline-day signing Wout Faes endured a chastening debut.
Until Son’s introduction and Leicester’s collapse, the Foxes arguably created as many chances as the hosts in the first hour, with Lloris notably saving well from Maddison and Patson Daka with the game in the balance.
But the Foxes’ talented attackers, even the again excellent Maddison, who brilliantly swept home Timothy Castagne’s cross to make it 2-2, simply cannot cancel out the volume of goals shipped at the other end.
It could have been more too. A Daka own goal was ruled out for a foul by Sanchez on Ward, who also tipped a header from the Spurs defender onto the bar later in the first half.