The South Korea global found the net for the fourth successive game, helping Spurs take a commanding lead in their last-16 tie.
'I think he was impressive in the first half but he lost that penetration instinct he has naturally. "My players are heroes", said Pochettino.
Pochettino's decision to pick Jan Vertonghen as a left wing-back against Dortmund paid off handsomely as the Belgian set up Son's opener before scoring the second goal himself. "What they are doing this season is unbelievable".
'Of course, we are happy now because it was a very good result but there is still a lot of work to do.
Reflecting on the second-half improvement from Spurs, Pochettino said: "The first half was very hard".
"We need to go out there knowing it's going to be so tough and we need to perform like we performed today, in our best way and try to think that we need to win the next game if we want to be in the next stage of the Champions League".
Harry Kane or Dele Alli are very important for us but we have players who can come in and do well. "If it was a different result, people might say I'm the worst coach in the world", he said.
Having been let off the hook after a potentially game-changing error by Foyth, Spurs did not pick up from there and continued their wobbly form for nearly the entirety of the first half.
This provided them with the base to score two more goals, inspite of what was a disastrous first-half showing.
"After that we played a bit too hastily".
Having had their own issues with injury and player unavailability in recent times, Tottenham Hotspur had been all but dismissed by the critics as no-hopers, both in terms of the title race as well as the Champions League.
Lloris made a superb save to deny Dortmund on the stroke of half-time as Dan-Axel Zagadou met Sancho's cross with a header that the Tottenham captain clawed out at full stretch.
Fernando Llorente managed to cap off a fine win three minutes later by nodding home a cross from Christian Eriksen as Spurs will take a healthy lead into the second leg.