"We should have got the ball forward rather than played from the back for their first goal".
The Bundesliga leaders, who were eliminated from the German Cup last week, were nowhere to be seen in the second half, with speedy teenager Jadon Sancho given no space to operate after the break.
Spurs will now travel to Dortmund for the return leg in a strong position, but Pochettino added: "For me, it's only the first leg and first half of the tie".
Son was not alone in earning Pochettino's praise, however, as the Spurs boss was ecstatic at the team's performance following a tough Premier League fixture against Leicester City on Sunday. He smiles and he creates energy in every single game. The Wembley crowd was there to see him in good numbers and the youngster did not disappoint, dancing past men nearly as if they weren't there at times in the first half. 'My players are heroes.More news: NASA Mars rover Opportunity finally bites the dust after 15 years
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Son started a brilliant second-half display in the last-16 first leg at Wembley by opening the scoring from Jan Vertonghen's excellent cross, before Vertonghen and substitute Fernando Llorente put Mauricio Pochettino's men on course for the last eight in the final seven minutes.
"We are happy now but still a lot of work to do".
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.
"I'm so happy for him, he was fantastic today", said the Argentine of his young countryman.
"3-0 is a very good result but at the same time we have to think that we have to finish the job".
"The first action was unbelievable - the people were pushing him, and then he made a few mistakes because he wanted to play".