Valle, who has successfully defended her world IBF belt five times, used her experience and advantage to beat Nhi by dominating most of the bout on Thursday night (local time).
Thousands of home fans in San Jose, Costa Rica cheered every time Valle threw an accurate punch.
In the first three rounds, Valle stormed Nhi with quick and fierce attacks. A better height and arm span than Nhi helped Valle deploy versatile strikes. She often aimed for Nhi’s head with powerful hooks. Even when Nhi defended her face with both hands, Valle still managed to hit the target.
The pace reduced in the fourth and fifth rounds but Valle still managed to dominate. She increased the intensity in the sixth round, forcing Nhi on defense. When Nhi tried to attack, she was countered and struck. She tried to knock out Valle in the 10th round but failed.
When the game ended, Valle ran around the ring to celebrate even before the referees gave the final score. All three referees gave the same score of 100-90 to Valley, perhaps the biggest point difference possible in boxing.
This is Nhi's first defeat in professional boxing after six matches, while Valle had 26 wins and only two losses.
Before the game, Nhi said she "brought one belt to Costa Rica and will come back with two." But in the end, she went home empty-handed and lost her WBO belt to Valle.
Nhi, 26, became the first Vietnamese boxer to win a world championship, after defeating Japan's Etsuko Tada last year.