Zamorano (14-0, 1 KO) has now made two world title defenses, barely four months after being elevated to assume unchartered territory as the sport's youngest reigning world champion.

Having pitched a shutout against Sana Hazuki on October 25, this was more competitive and the scorecards were still rather one-sided after 20 minutes' action, much to the frustration of some critics on social media.

Local judge Adrian Aguillon Meza had her winning virtually every minute (100-90), while fellow Mexican Martin Canizalez (98-92) and California's Edward Collantes (97-93) were more complimentary in the Argentine's favor.

Unafraid to trade in the pocket, negating her physical advantages, Zamorano looked slick en route to an early lead on the scorecards through six rounds.

Ruiz's smile of acknowledgement said all you needed to know in the early going, throwing plenty but being undone by Zamorano's jab and combination punching at mid-range. Whenever she strayed away from the high defensive guard, the teenager looked to punish her with a variety of flurries from uppercuts and hooks to work downstairs.

The 28-year-old (7-3-1) needed to keep their exchanges at short-range but maintaining offensive discipline to do so was an exhausting task.

Sneaky body shots scored for the champion in rounds two and four, while Ruiz amusingly wheeled away to celebrate a faux knockdown midway through round three when Zamorano lost her footing. The challenger's arms weren't aloft for long.

Zamorano always looked for the final say whenever they engaged in close quarters, to land first and last, while being skilled enough to have the freedom of choice: wade into the fire or sidestep it.

Camila chants reverberated around the champion's hometown as she unloaded more work in the sixth, an undeterred Ruiz nonetheless persisting with her forward pressure to throw punches and keep her on the move.

Even if the three scores didn't show it, Ruiz's endeavor worked a treat down the stretch as Zamorano didn't have matters all her own way. Judging from the first few rounds, you could be forgiven for thinking so.

Being tagged with more shots in the previous two frames only encouraged Zamorano to stand and trade during a fiery ninth round, rather than box smart and use her physicality to keep Ruiz at the end of her punches.

The final stanza had flashes of fury but while Ruiz climbed the top rope to celebrate in her corner after the final bell, it was the 18-year-old who emerged victorious after a deceptively difficult evening's work.