Son was introduced from the substitutes’ bench, and he ended up grabbing a late winner for the Lilywhites.
The South Korean international cleverly flicked the ball in from a Kieran Trippier cross in the last minute, and Pochettino was delighted with the forward’s performance.
“It’s important for him and important for us," Pochettino said. "We have a strong squad and every player is important. Today we showed that again, coming from the bench Son made a real impact and scored a crucial goal.”
Tottenham had taken the lead against Watford when Erik Lamela capitalised on a defensive mistake, but they were pegged back by the hosts.
Odion Igholo netted an equaliser for the Hornets, and they held firm for much of the contest - even after Nathan Ake was sent off.
However, Spurs’ numerical advantage eventually paid dividends, with Son’s winner sparking wild celebrations.
The 23-year-old made a blistering start to his Tottenham career, but this was his first goal in 13 outings.
Tottenham’s win at Vicarage Road has moved them up to third in the Premier League table.