Rosas Jr. acquired a record of 5-0 competing exclusively in Tijuana, Mexico for the Ultimate Warrior Challenge promotion winning all five fights by stoppage inside of two rounds.[2]
Dana White's Contender Series Season
Rosas Jr. was then booked to compete on Week 9 of Season 6 of Dana White's Contender Series on September 20, 2022, against Mando Gutierrez.[3] He would win the fight via a dominant unanimous decision and was awarded a contract by Dana White thus becoming the youngest fighter to sign a contract with the UFC at the age of 17.[4]
Ultimate Fighting Championship
After earning his contract, Rosas Jr. made his UFC debut at UFC 282 against Jay Perrin on December 10, 2022.[5] He won the fight via first round submission and this became the youngest person to ever win a UFC fight.[6] This win earned him the Performance of the Night award.[7]
Rosas Jr. faced Christian Rodriguez on April 8, 2023, at UFC 287.[8] At the weigh-ins, Rodriguez weighed in at 137 pounds, one pound over the bantamweight non-title fight limit. His bout proceeded at catchweight and he was fined 20% of his purse which went to Rosas Jr.[9] He lost the fight via unanimous decision.[10]
Rosas Jr. was scheduled to face Ricky Turcios on February 24, 2024, at UFC Fight Night 237.[14] However, Rosas Jr. was forced withdraw just before the bout was expected to begin due to an illness. As a result, the bout was initially pushed back one week to UFC Fight Night 238 on March 2, 2024.[15] In turn, the bout was ultimately scrapped for unknown reasons.[16] The fight would then be rescheduled to UFC on ESPN 57 on June 8, 2024.[17] He won the fight via rear-naked choke in the second round.[18] This win earned him the Performance of the Night award.[19]
Rosas Jr. faced Aori Qileng on September 14, 2024, at UFC 306.[20] He won the fight by unanimous decision.[21]