Alvarez, who is undefeated in 40 professional fights, retained his WBC light middleweight title and remains the youngest middleweight title holder at age 21.
The young champion from Gudalajara, Mexico, had spent the first three rounds feeling out Citron and in the fourth round he started unleashing power shots that sent Cintron down the canvas but was later saved by the bell.
At the start of the fifth round, Cintron came in strong and caught Alvarez with some power punches, but the unbeaten champion got him with real straight power shots forcing the referee to stop the fight seven seconds before the end of the fifth round.
All three judges had the fight 40-35
on the cards.
Later, Alvarez called out his fellow unbeaten boxer Floyd Mayweather, Jr. saying he wants to fight the best.
"Next year we want the best, we want Mayweather in May," he said.
"Apart from the money, we want to fight the best in the world and he's the best pound for pound, so we want to fight him."
Cintron, who is from Puerto Rico and a former light middleweight champion suffered his fifth loss in 33 professional fights.