The 42-year-old wrestler lost to former UFC Hall of Famer (and former Light Heavyweight champion) Tito Ortiz at Combate Americas 51 in McAllen, TX.
Ortiz forced Alberto to submit to a rear naked choke at 3:10 of the first round.
Ortiz had vowed to donate $10,000 to the charity of Alberto's choice if the former WWE star could make it past the first round.
The bout was fought at an agreed-upon 210 pound catchweight, as Ortiz has fought primarily at light-heavyweight through his career, and Alberto at heavyweight.
The win improves the 44-year-old Ortiz's record to 21-12-1 in his career, while Alberto falls to 9-6.
The defeat marks only the second time Alberto has been submitted in his MMA career. The first instance came in March 2002, when he lost via rear naked choke to Kengo Watanabe in Nagoya, Japan.
Alberto's most recent fight prior to Saturday night, came in February 2010, mere months before he debuted on the WWE main roster. There, he lost via TKO to Yamamoto Hanshi at an event in Madrid, Spain.