The 34 year-old, who previously reigned at minimumweight and light-flyweight, out-pointed Komgrich Nantapech in just his second bout at the weight limit to pick up the vacant flyweight strap.
Nietes, who now boasts a 40-1-4 C.V, showed little signs of struggling after moving up the necessary four pounds from making eight title defenses at 108.
In the end, judges scored 117-111 (twice) and 115-113 in favor of the Filipino, who improved his pound for pound ranking with yet another win in a world title fight.
Nantapech dropped a fourth loss in 26 contests and will need to regroup on the back of what was a first taste of world level for the Thai fighter.
