Reece McFadden produced an outstanding performance to give Scotland's boxing team a massive boost on the first day in the ring at Glasgow's SECC.
The 19-year-old from Motherwell, the seven-time Scottish champion, had the arena rocking as he
Earlier, there was dejection as the first of the Scots trio to fight on Friday, Lewis Benson, to New Zealand's Bowyn Morgan.
The contrast in emotions for the team-mates could scarcely have been greater.
Between those bouts, there was a win for another Motherwell fighter, Ross Henderson, in the +91kg division. He was too strong for Parveen Kumar of India.
The broad smiles on the faces of the Scotland coaching team, Mike Keane and Craig McEvoy, signalled just how remarkable McFadden's victory was.
They knew that for the Forgewood fighter to reach the last 16 of the 52kg division he would need to produce something special against the favourite for the gold medal.
"This gold is mine. This gold is my medal," McFadden told BBC Scotland after the bout.
"That was the best in the world in there. He couldn't handle it.
"I'm a strong wee guy. I do lots of weights in my house constantly. It was the performance of my life and I enjoyed it. It was brilliant."
Former WBO world super-featherweight champion Alex Arthur suggested to the teenager on Thursday that the best way to approach the fight was to show Selby no respect.
That became evident as cocky McFadden, the squatter of the two boxers, moved in and out of range at speed and used his reflexes to evade the Welshman's attacks to launch his own.
Arthur said: "His tactical approach to the fight was perfect. He made a great start, he never rushed in. He waited patiently. He made Selby miss and counter-punched him.
"Now he has to stay focused. He has to understand he has a lot more fights ahead of him, that this wasn't the final and that's going to be very difficult for him.
"He will be sky-high with confidence. I wouldn't like to be his next opponent, because he is on fire.
"He's got probably the most difficult draw in that weight division. He fights Charlie Edwards next."
Scottish champion Benson to make the team and was desperate to reach the latter stages.
However, after a bright first round and a half, the Lochend fighter took a heavy left hook to the jaw and was thumped again later in the round.
"I got hit," said a dejected Benson. "I was boxing away quite nicely and I was happy with my performance in the first round.
"In the second round I came in nicely again but I got caught.
"I believe I came back and won the last round but the judges didn't see it like that.
"The coach said to me in the corner, 'watch your right hand' and I dropped it. It's tough to take."
Henderson, who reached the last 16 in Delhi four years ago, used his power to good effect against Kumar.
"He's a very tough fighter. He keeps coming forward," he said of the 99kg Indian.
"He's a good puncher and I got caught with the back hand.
"I didn't know at the start if he was southpaw or orthodox so I had to adjust straight away. That's the third time I've been in with a southpaw and the first time I've beaten one and there's no better stage.
"I'm over the moon I've got the win. I'm 18 and a half stone. I'm a big, fit man. We train hard at Boxing Scotland. I want to thank the coaches."
Henderson now faces the big-hitting Englishman Joseph Joyce on Tuesday in the quarter-finals.