Bayer Leverkusen attacker Son entered the record books as the first South Korean player to score a treble in one of the top European leagues, however it came against his former club of four years - Hamburg - as the 21-year-old's side came away with a 5-3 win.
That fact, Son said, was a blip on the feat.
"It also makes me feel a little hurt and sad because HSV (Hamburg) are my former club," Son told Bundesliga.com.
"Of course though, it was the game in which I scored my first Bundesliga hat-trick, but I can still enjoy it a little bit."
The South Korean marked himself harshly, too, as he rued erring in the lead-up to Hamburg's third goal, before ensuring Leverkusen of the three points by scoring their fifth.
"We haven't managed to score that many goals in a single game so far this season," Son said.
"I'm delighted with the win.
"However, I'm still annoyed with the mistake I made in the lead-up to their third goal.
"I was really upset about that but fortunately we were then able to score the deciding goal on the counter to make it 5-3."
Son, who had just one goal to his name this season prior to his ground-breaking treble, said he tried to keep calm heading into his eighth start for Leverkusen's head coach Sami Hyypia.
"I wanted to go into the encounter feeling more relaxed. Having fun is part of football," Son said.
"I have to thank my team-mates and the coaching staff who have given me a lot of self-confidence.
"The head coach told me that I shouldn't be putting so much pressure on myself, because I'm only in my first season with Leverkusen.
"It all helped me produce a top performance today."
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