The former Fratton favourite was casually asked about the moment during his appearance on the latest edition of Pompey Talk: The Podcast.
The now Barnsley striker was in typical jovial spirits as he recalled his Blues days, reminiscing about the club’s League Two title win and providing some amusing anecdotes before his departure in August 2018.
However, the ever-smiling Chaplin adopted on a more sombre perspective when events from that March 18, 2017, game at the Lamex Stadium came up in conversation.
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Pompey were trailing 3-0 at the time and were offered the chance to score a late consolation from the penalty spot when the then 19-year-old was brought down in the box.
The popular teenager stepped up to take the spot-kick, but was left with egg on his face when his Panenka effort floated into the arms of wily veteran keeper Chris Day.
The miss failed to matter in the grand scheme of things.
Pompey still lost the match but went on to win seven of their eight remaining matches to claim the League Two title.
Nevertheless, Chaplin admitted it was something he’ll never do again in his career, having been taught a serious lesson.
He revealed: ‘Take away the semi-final against Plymouth that we lost and that's probably the worst thing that's happened in my career, like honestly.
‘As a personal feeling, definitely yeah, but it's something that I've learned from as well.
‘Obviously, I was only young, and I'll learn from it, but I'll never put myself in that position ever again.
‘Not to take a penalty, obviously I'll take a penalty, I'll happily take a penalty whenever I can.
‘But I'll never do something like that ever again. Never.’
When asked how memories of the incident makes him feel now, the Blues academy graduate added: 'Embarrassment... yeah, that's probably the main one.
‘Naivety is definitely up there as well, because I remember I said to Robbo (Gary Roberts), “let me have it”, and I said to him I wanted to go down the middle, because we always said in training the middle was such a safe penalty, the goalkeeper always has to dive.
‘Obviously, I didn't miss the target or anything like that, but I just think, you cannot be 3-0 down in a game and chip a penalty, like you can't do that. You just cannot do that.
‘If I'd run up and hit it as hard as I can, keeper didn't move, it's fine. No-one would say anything to you.
‘But, yeah, genuinely in my head, as an 19-year-old, I just thought that the safest way of scoring a penalty was going down the middle, and then the keeper was about 44-year-old and just never moved, obviously couldn’t ne bothered - 3-0 up, the game's done, like I'm not moving!
‘Obviously, that's one of the worst memories of my career so far, definitely.’
Chaplin revealed manager Paul Cook spoke to him after the game in front of his team-mates.
He offered the then-teenager some words of advice – guidance he still abides by to this day
‘It was horrendous. In the dressing room after wards Cookie was actually great,’ added Chaplin, who scored 25 goals in 119 Pompey appearances.
‘He said to me in front of the lads, "you can't do that, you need to learn from that, you need to respect the players that you're playing with and the team as well as there’s other players who could have taken that penalty and scored”, so obviously there's things like that.
‘So yeah, it's something that I'll definitely learn from.
‘Obviously, it's a good thing from that aspect, looking back.
‘But in terms of one of the worst feelings in my life, it's definitely up there.’
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