Welterweight Evans produced a sterling display to come from behind and claim an 11-7 win over the fourth seed Lithuanian Egidijus Kavaliauskas.
Evans, who alongside Selby became the first Welsh boxers for 86 years to win European gold last year, was proud to progress and prove a point over his favoured opponent.
"It was unbelievable,” said the 21-year-old. “The crowd was cheering for me, and obviously I had a point to prove to this opponent.”
The pair met in Baku at the world championships where it was Kavaliauskas who came out on top, but this time it was Evans who was the victor inside a raucous ExCel Centre.
"I fought him in the world championships and that was the kid I lost to,” he said. “I wanted to box him again to prove a point.
"But the result at the worlds didn't play on my mind at all (during the match).
"I was expecting him to come at me. I was down in the first round. It was a terrific last round.
"I will be a bit more used to this. Fight by fight I tend to improve. Hopefully I can come back with a medal."
Next up for Evans is Custio Clayton, who is within one win of claiming Canada's first boxing medal in 16 years
In two strikingly similar welterweight bouts, Clayton and Evans were level with their second-round opponents going into the final round before streaking away.
Canada last won a medal, a silver, at the 1996 Atlanta Games eight years after Lennox Lewis, a dual citizen who went on to win multiple world professional heavyweight titles for Britain, won its last gold.
In the evening, Selby booked himself a place in the last eight with a nervy but impressive win over Kazakhstan’s Ilyas Suleimenov.
The Welsh flyweight led from the front and despite incurring a warning in the final round, ran out the 19-15 winner – and is now only one fight away from a guaranteed Olympic medal.
World number one Selby, who claimed a silver medal at last year’s World Championships in Baku, said he will go from strength to strength after a slightly untidy opening bout.
"I didn't feel at my best tonight and I was sloppy, but as the competition progresses I will get better,” he said.
"I just had to hit and move to win. The referee thought I was holding behind the head and grabbing, but it was him.
"I can and will box out of my skin from now on.
"I am buzzing now, especially as my mum was in the crowd. It was only the second time she has seen me box. She usually comes to the fights, but goes outside when it is my turn."
The atmosphere inside the ExCel Arena was parallel to a world title fight at times and Selby’s coach Dave Alloway said he will only get better from experiencing such raucous home support.
"It was a nervous one and his timing wasn't right, but now he has experienced the noise of the crowd he'll get better,” he said.
Both losing semi-finalists get bronze in Olympic boxing.
Clayton, who surprised Mexican Oscar Molina Casillas in Sunday's first round, stayed patient through a cagey opening two rounds with Cameron Hammond but used his quick feet and jab to counter the Australian's longer reach to take the contest 14-11.
World amateur champion Taras Shelestyuk of Ukraine also eased through to the quarter-finals where he will face Beijing bronze medallist Alexis Vastine of France, who sneaked past Mongolia's Tuvshinbat Byamba.
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