As a riposte, it was about as emphatic as they come. Son Heung-min was actually stumbling, the loose ball ricocheting awkwardly between his legs, when a section of the Millwall fans situated in that nearby corner of the arena began bellowing their latest chorus of “DVD”. He had to edge back rather apologetically towards the touchline to gather but, with Jake Cooper wary of darting from the penalty area, there was still time to readjust, wriggle towards the edge of the penalty area and curl his shot gloriously into the far corner beyond Tom King.

The taunts rather stuck in the throats thereafter. Whether the South Korean knew what was being sung remains unclear, but there has long been a perception that the chant, together with the accompanying “He’s selling three for a fiver” which was also given an airing here, is racist when aimed at Asian footballers. Paul Ince, then captain of Wolverhampton Wanderers, had described a “small section” of Millwall fans as “an absolute disgrace” for identical songs spat at his team-mate Seol Ki-hyeon in a league fixture at the Den 12 years ago. This time round it was Kyle Walker, sat among the Tottenham Hotspur substitutes, who made his disgust clearest. As the home players descended upon Son out on the pitch, the England right-back sprung up himself in celebration while pointing angrily towards the away support.

The Football Association, which continues to scrutinise the post‑match events in SE16 from Millwall’s fifth‑round victory over Leicester City, will await the referee’s report and observations from both clubs and the police, but is understood to be aware of the issue. Whether it chooses to pursue a collective, rather than target individuals, remains to be seen, but an investigation of some kind will follow to ascertain whether sanctions are necessary. The FA should probably also consider the home fans’ discriminatory chorus of “No noise from the Pikey boys” which erupted around the ground during thatfractious first half.

“I didn’t hear anything but, if that’s proven to have happened, we won’t condone that,” said the visitors’ manager, Neil Harris. “We came here in the right spirit, to enjoy an FA Cup quarter-final. I’m sure it will be left to the authorities. We just want people to enjoy the game: Mauricio Pochettino wants to be talking about his team’s quality, and we don’t want anything drawing the focus from what we’ve achieved in this competition. [Incidents like that are] wrong in society, and it’s wrong in football.”

Son, for his part, has already had his say. Seol had scored a last-minute winner back in 2005 to deflate and defeat Millwall. His compatriot’s response was just as resounding. That whipped finish beyond King was the first goal of a maiden hat-trick for Spurs, goals to offer Pochettino hope that the ankle injury suffered by Harry Kane early on, which could threaten his involvement over a large chunk of what remains of the campaign, might not prove terminal to this team’s pursuit of silverware and a top four finish. Life without Kane, of course, had been distinctly unappealing back in the autumn. No one could truly fill the void left by the Premier League’s top scorer, but at least Son goes into this next run of games in buoyant form.

The finish for the second, a volley dispatched on the gallop as he latched on to Kieran Trippier’s lofted pass into the space behind Cooper, was magnificent, an instinctive connection to showcase of his talent. King, an inexperienced goalkeeper who spent time on loan at Welling and Braintree last season, looked emotionally shot after a torrid afternoon by the time Son’s effort dribbled through his hands in stoppage time at the end.

That was the South Korean’s 14th goal of the campaign, and sixth in this competition. His inconsistency can infuriate at times, as was evident from Dele Alli’s hissy fit in the centre at that poor first touch in the buildup to the opener, but this is a player upon whom Spurs will have to rely in the weeks ahead. “It’s about the team performance, whatever names and players are out there,” said Pochettino. “My job is to select only 11 players in every game, but I was always happy with Sonny. He can play like a striker. One of our best performances was against Manchester City here [in October], and he was the main striker when Harry was injured first time round. We have different opportunities to play, or to use different formations.

“I’m sad about Harry, but now it’s about trying to find a solution and seeing who is the best player to replace him. It was important the players who play in Harry’s position, Sonny and Vincent [Janssen], who haven’t played much in the last few weeks, find the net and score goals. They may now be important for us.” Janssen’s reward had been his first from open play in 1,134 minutes of first-team football for this club since joining from AZ Alkmaar last summer. True to form, and forever the focus, it had been Son who provided the assist.