Lucas Santamaria turned in the upset on the Jamal James-Thomas Dulorme card Saturday at Microsoft Theater in downtown Los Angeles.
Santamaria put the more-experienced Mykal Fox down in the first round and maintained the pressure to win a unanimous decision in a 10-round welterweight fight on the FS1 telecast. The scores were 99-90, 97-92 and 96-93.
Santamaria (11-1, 7 KOs) had not faced an opponent of Fox’s caliber before Saturday.
Fox (22-2, 5 KOs) had won three in a row since losing a decision to unbeaten Uzbek Shohjahon Ergashev in May of last year.
In other fights on the card, Michael Polite Coffie (10-0, 7 KOs) put Luis Eduardo Pena (6-1, 6 KOs) down and stopped him at 1:35 of the fifth round of a scheduled six-round heavyweight bout.
And 18-year-old Vito Mielnicki (6-0, 4 KOs) knocked out Chris Rollins (3-2) at 2:19 of the second round of a scheduled six-round welterweight fight.