Giovani Segura conceded much to land his fight with junior flyweight champ Ivan Calderon, but he still had enough advantages — namely youth, size and power — to hand the aging boxing master his first loss in a rousing back-and-forth struggle on Saturday.

Segura (25-1-1, 21 knockouts) stopped Calderon (34-1-1, 6 KOs) in the eighth round of their 108-pound showdown in Guaynabo, Puerto Rico, overcoming the slick 35-year-old veteran’s superior skill, technique and ring generalship with dogged determination and non-stop punching.

The Southern California-based Mexican took short money, traveled to Calderon’s hometown and fought the stick-and-move specialist in a 24-by-24-foot ring in order to get his shot at the undisputed junior flyweight title.

His gamble paid off. Segura unified two alphabet belts and claimed THE RING’s 108-pound championship with the best performance of his career, but his victory did not come easy.

Segura expected the anticipated pure-boxer-versus-pure-puncher matchup to be as mentally intense as it would be physically taxing and he was right. The 28-year-old southpaw slugger’s patience and strategy was just as integral to his victory as his vaunted punching power.

Calderon (34-1-1, 6 KOs) easily out-jabbed and out-maneuvered Segura in the early rounds of bout, but the puncher calmly stalked his fellow southpaw while methodically attacking the constantly moving boxer’s body.

Calderon landed the cleaner punches in the first three rounds, but Segura was clearly in the fight and systematically slowing the older man down by aiming hard rights and lefts at the hometown favorite’s midsection.

Calderon thrilled the packed arena by staying in the pocket and trading punches with Segura in the fourth round, but the veteran might have committed a tactical error by standing his ground.

Or perhaps Calderon, who has noticeably slowed down in recent fights, simply got “old” under Segura’s constant pressure. Calderon, a member of Puerto Rico’s 2000 Olympic squad, had boxed in 20 alphabet title bouts going into the Segura fight. He’s gone the 12-round distance 14 times in his near-10-year pro career. That’s a lot of miles on 35-year-old legs.

And don’t think Segura wasn’t aware of that fact. While Calderon landed head-twisting left crosses in the fourth, Segura punctuated the round by banging the veteran’s hips.

The brutal body attack paid off in the fifth round when Calderon tried to catch a breather against the ropes and was relentlessly worked over by Segura until he slipped to the canvas. Calderon got up on unsteady legs and continued to take a beating until the end of a round that could have been scored 10-8 in Segura’s favor despite no official knockdown being called.

However, Calderon wasn’t ready to let go of his crown. The champion rallied in rounds six and seven, rocking Segura in his tracks with flush left crosses and right hooks. Calderon looked sharp as he got back on his toes and boxed in his usual stick-and move style but there was a sense of urgency in his facial features and body language seldom seen in his fights.

Segura’s constant pressure, high-volume punch output and perhaps his greater size — the junior flyweight standout typically puts on 10 to 12 pounds after weighing in — made Calderon feel his age.

And the sweet scientist definitely looked old in the eighth round when Segura crowded him into a corner and overwhelmed him with power shots to the head and body until he took a knee. An uppercut stunned Calderon before he dropped down but a series of sweeping rights to his aching side convinced him to stay on his knee for the referee’s full 10 count.

It had to have been a difficult decision for the proud Puerto Rican to lose in that fashion but he has no reason to hang his head in shame.

For 9¾ years he took on many of the sport’s top strawweights and junior flyweights — including former titleholders Alex Sanchez, Roberto Leyva, Daniel Reyes, Isaac Bustos, Nelson Dieppa and then-reigning RING champ Hugo Cazarez — and always emerged victorious.

Calderon’s sharp mind, accurate punching and fleet footwork enabled him to outbox much bigger and far-more powerful fighters, such as Cazares, who currently holds a 115-pound title.

Against Segura, his mind was as sharp as ever and his punches were on the mark but his legs were no longer able to carry out his will.