Dele Alli was left out of the squad for a second successive game after being hauled off at half-time in Tottenham’s opening day defeat to Everton, while Tanguy Ndombele was handed his first start of the season.
Tottenham thought they were ahead with just three minutes on the clock, with Harry Kane acrobatically volleying home after Matt Doherty’s header into the box. The goal was disallowed after a lengthy VAR check, however, with Son deemed marginally offside.
Southampton had a goal disallowed of their own swiftly after, though this decision was significantly more clear cut. Danny Ings clearly handled Hugo Lloris’ headed clearance, his subsequent pass into an empty net correctly ruled out.
And though Kane had another goal waved off for offside, it was Southampton who finally took the lead, Ings latching onto a floating Kyle Walker-Peters ball over the top and firing into the far bottom corner.
Tottenham levelled with seconds remaining of the first half, however. Ndombele bamboozled the Saints defence with a dazzling pirouette, before finding Kane down the left, whose first-touch left-footed ball sent Son on his way to fire beyond Alex McCarthy.
There was no stopping this inspired partnership there, however, as Kane found Son once more with a pin-point cross that Kevin De Bruyne would of, which the South Korean controlled with his chest before dispatching with his left foot.
From provider to scorer, Kane put the finishing touches on the match, poking home after substitute Erik Lamela hit the post.
Southampton were awarded a controversial penalty with minutes remaining after the ball struck Matt Doherty’s arm, which Ings slotted home for his second of the game.
A highly confidence-boosting victory moves Tottenham back into the top half, and with the London club in the midst of a hectic schedule, Jose Mourinho will have been delighted to have seen Son and Kane in such telepathic form.