Early mixed martial arts career

Pacio made his debut at Team Lakay Championship 8,^[7] where he came away with a first round TKO over Denver Songaben. This would be a start off red-hot six-match winning streak which eventually led to him being signed by ONE Championship.

He made his ONE Championship debut on April 15, 2016 - beating compatriot Rabin Catalan by second-round technical knockout at ONE Championship: Global Rivals at the Mall of Asia Arena in the Philippines.^[8]

After beating Kritsada Kongsrichai, Pacio earned his first shot at the ONE Strawweight World Championship against Yoshitaka Naito at ONE Championship: State of Warriors on October 17, 2016 in Yangon.

Pacio came close to being a World Champion at age 20, as he punished Naito with his patented Wushu strikes on the feet, but a mishap in the third round cost him the entire match as he got submitted by the Japanese via rear naked choke.^[9]

First World Title reign

After his loss to Naito, Pacio would wreak havoc in the division - winning five of his next six bouts to book another date with Naito this time at ONE: Conquest of Heroes on September 23, 2018 in Jakarta Indonesia.

Pacio rematched Yoshitaka Naito at ONE Championship: Conquest of Heroes on September 22, 2018. Pacio looked more confident in the rematch as he stuffed Naito's takedowns for much of the first two rounds while punishing him on the striking department with lightning quick kicks and combinations from different angles. The Japanese did finish strong as he scored takedowns on his younger opponent, but Pacio stayed busy even on his back - earning all of the judges' nod to get a unanimous decision victory.^[10]

Losing the belt, Second reign

Pacio's reign, however, would not last long as he dropped his belt four months later to Yosuke Saruta at ONE Championship: Eternal Glory on January 19, 2019, in a controversial split-decision.^[11]

The Japanese pushed the action while Pacio opted to pick his spots and counter in one of his more tactical bouts yet. In the end, two of the judges favored Saruta's aggression - crowning him the new ONE Strawweight World Champion.^{[citation needed]}

With a close finish, Pacio was given an outright rematch at ONE Championship: Roots of Honor in Manila on April 12, 2019 ^[12] Pacio did not disappoint as he scored a sensational fourth round knockout win with a well-timed knee to regain his lost title.

Later that night, ONE Chairman and CEO Chatri Sityodtong announced that there would be no need for an immediate trilogy after Pacio's definitive win.^[13]

Pacio defended his belt for the first time in his second reign as he takes on compatriot Rene Catalan at ONE Championship: Masters of Fate in Manila on November 8, 2019.^[14] He defeated Catalan via arm-triangle choke in the second round.^[15]

Pacio defended his title again against Alex Silva at ONE Championship: Fire and Fury on January 31, 2020. He won the very close bout via split decision.^[16]

Pacio defended his ONE Strawweight World Championship in a trilogy match against Yosuke Saruta at ONE Championship: Revolution on September 24, 2021.^[17] He won the bout via TKO in the first round.^[18]

Pacio was expected to make his fourth title defense against the #1 ranked strawweight contender Jarred Brooks at ONE 158 on June 3, 2022. The bout was eventually postponed, as Brooks withdrew from the fight due to an injury.^[19] The fight was rescheduled at ONE 164 on December 3, 2022.^[20] Pacio lost the fight and the belt by unanimous decision, making him and the Philippines had no more Filipino World Champions of any weight classes.^[21]

Post-championship and Third reign

Pacio faced Mansur Malachiev on October 7, 2023, at ONE Fight Night 15.^[22] He won the fight via unanimous decision.^[23]

Pacio faced Jarred Brooks for the ONE Strawweight World Championship in a rematch on March 1, 2024, at ONE 166.^[24] He won the title via disqualification due to illegal slam in round one.^[25]