After a tough start at White Hart Lane, Dele Alli opened the 33rd minute with a stunning curling finish as Spurs collected their 11th consecutive home victory.
Eric Dier added a second six minutes later as Spurs took control, while Son put the result beyond any doubt just before half-time with a wonderful curling effort from outside the box.
The South Korean crashed in his second on the volley in the 54th minute before Harry Kane made his return on a perfect day for Spurs.
Tom Collomosse was at White Hart Lane to assess the key talking points...
No Kane, no pain
When Harry Kane is fully fit, he plays. Mauricio Pochettino said on Friday that his 24-goal top scorer was as important to Tottenham as Lionel Messi is to Barcelona.
Few would argue with that assessment – yet Spurs have proved recently that they can prosper in his absence. The score was 0-0 when Kane’s ankle ligament problem forced him off early in the FA Cup quarter-final against Millwall.
Spurs won 6-0. They won their next three matches, too, scoring seven goals and conceding two. They were 4-0 up here when Kane replaced Vincent Janssen after 61 minutes.
Kane is key – but this no one-man team.
Keep Son or return to 3-4-2-1?
With Kane fit again, here is the conundrum for Pochettino. Does he revert to Tottenham’s most effective system, or stick with 4-2-3-1 to keep Heung-min Son in the team?
Tottenham have looked more fluent and dangerous going forward when they use 3-4-2-1, yet that would probably mean leaving Son on the bench as Kane, Alli and Christian Eriksen occupy the three forward roles.
Logical enough, but then look at the numbers: in Kane’s absence, Son has scored seven times in four matches. It would be a brave manager indeed who was happy to leave a record like that on the bench.
It was a great source of frustration to Pochettino that when Tottenham were pushing Leicester in the title race last season, his side frequently kicked off later than the eventual champions.
Indeed, in six of seven rounds of matches in the spring, Leicester took the field before Spurs. While the schedule is not as controversial this season, today’s was the first of two consecutive lunchtime kick-offs for Spurs.
This win put Spurs momentarily four points behind leaders Chelsea – and next weekend, Pochettino’s men start at 12.30pm once again, this time against Bournemouth at White Hart Lane.
Will it be enough to make Chelsea wobble?
Watford lack staying power
The visitors were perfectly competent for the opening 20 minutes, keeping Tottenham at bay and breaking effectively when they had chance.
Two free-kicks from the left from Jose Holebas caused problems. Yet as soon as Spurs established a grip on the game, there was no sense Watford had an answer.
Dele Alli’s opening goal finished off a marvellous move, yet for the second and third – scored by Eric Dier and Heung-min Son respectively – some of the defending was half-hearted.
Yes, the Hornets were missing key players due to injury and suspension, but boss Walter Mazzarri was entitled to expect a little more determination from his team.
Taylor’s brilliant call
Referees are usually the punch-bags of players, managers, fans and media – so let’s hear it for Anthony Taylor today.
With the score 0-0 shortly after the half-hour mark, Abdoulaye Doucoure manhandled Mousa Dembele to the floor as the Tottenham midfielder burst into the Watford half.
Pochettino berated fourth official Lee Mason when the foul was not called – but Taylor had played a clever advantage.
Sure enough, Eriksen found Son, who set up Alli to curl the ball past Heurelho Gomes from the left corner of the penalty area.
Pochettino celebrated – then sheepishly turned to Mason to acknowledge Taylor’s superb decision.