After classy Roniel Iglesias Sotolongo won Cuba's first Olympics boxing gold in eight years on Saturday, a long wait for the great amateur boxing nation, Carrazana, 18, added boxing gold number 34 with a sumptuous display.
Cuba's boxing golds make up almost half of their total Olympics successes and it was easy to see why as Carrazana again sized up his opponent in the opening exchanges before taking a tight first round that proved a battle of the left hooks.
The silky southpaw, who eased through the draw, beating second-seeded Briton Andrew Selby in the process, soaked up more pressure in the second round, evading much of what was thrown at him to keep his narrow lead going into the last.
Both boxers also landed punches after the bell had sounded at the end of the second, giving the final round an added edge.
The fight opened up a little more as Carrazana began flinging and landing left upper cuts, but Nyambayar, who upset world champion Misha Aloian of Russia on his way to the final and was hoping to add to Enkhbatyn Badar-Uugan's first Mongolian boxing gold four years ago, could not get through the quick Cuban's defence.
Carrazana fell to his knees when the final score of 17-14 was called before dancing around the ring, showboating a little by demonstrating a few push-ups and following Sotolongo in taking a lap of honour with the Cuban flag.
Losing semi-finalists Michael Conlan of Ireland and Russia's Aloian took bronze.
Ukraine's Vasyl Lomachenko showed why he is regarded as the best pound-for-pound fighter in the amateur ranks when he showed no ill effects in moving up to lightweight to romp home to a second successive Olympic gold.
Lomachenko was just about the hottest favourite of the London Games after he followed up the featherweight gold he won with ease in Beijing with a world title apiece at both feather and lightweight class.
It was the same story in London when he rarely had to move into top gear despite moving up a class and he had too much for South Korea's Han Soon-chul, easing to a 19-9 win in front of compatriot and world professional champion Vladimir Klitschko.
The irrepressible Lomachenko was in a different league to the Korean, taking the first round 7-2 with fierce right and left upper-cuts, punishing body shots topped off with sleek footwork that is almost unmatched among the amateur game.
The 24-year-old Ukrainian, who sports a tattoo of his father and coach Anatoly's face on his abdomen, continued boxing the kind of fight that would please any coach, keeping Han at bay to widen his lead by a point.
He was able to take his foot off the gas in the final round and coast to a victory.
Lomachenko, who will join the Olympic boxing governing body's professional league next year meaning he will still be eligible to go for a third gold in 2016, cracked his first smile of the Games when the result was announced.
Putting two fingers in the air to acknowledge both his second gold and the second for Ukraine at the Games, Lomachenko was hugged by Klitschko as he left the ring draped in the Ukrainian flag.
"I'm really proud of my countryman Lomachenko, it is not a common thing to win two times," Klitschko said from ringside. "It would be really exciting to see him in a professional ring."
Losing semi-finalists Yasniel Toledo Lopez of Cuba and Evaldas Petrauskas of Lithuania took bronze.