Isaac Chilemba was knocked down twice but got up to defeat Maxim Vlasov on points in Tulsa, Oklahoma, on Friday night.
On the undercard, South African Simpiwe “V12” Vetyeka knocked out former IBF minimumweight champion Roberto Leyva in the third round.
Malawi-born Chilemba, who now fights out of Johannesburg, won the super-middleweight bout 95-94, 96-92 and 96-92. It was his first fight outside Africa.
Chilemba used his well-honed skills to outbox Vlasov through most of the early rounds but the aggressive, go-forward tactics of the Russian probably earned him some points on the official cards.
The rather awkward Russian seemed to be trailing going into the eighth round. But when he knocked Chilemba down twice in the eighth round he appeared to be on the road to victory.
Chilemba showed his inexperience by jumping up immediately on both occasions instead of taking the count of eight, but he fought back courageously before the end of the round.
Vlasov appeared to have punched himself out and the superior boxing skills of Chilemba prevailed at the end of an exciting fight.
The 23-year-old Chilemba improved his record to 16-1-1, including eight knockouts. Vlasov dropped to 19-1; 10.
VETYEKA SHOWS HIS CLASS
Vetyeka, a former SA bantamweight champion, knocked out Levya with a booming body blow to improve his record to an impressive 22-1, with 13 short-cut victories.
The South African, who had weighed in at 54.88 kg, was in outstanding form as he defeated the rather podgy former IBF minimumweight champion.
The fight, scheduled for six rounds, was over 2 minutes 32 seconds into the third round.
The 30-year-old Vetyeka dominated from the first bell before landing a short right to the body in the third round. It left the southpaw Leyva, 31, clutching his side in agony as the referee counted him out.
Leyva, a Mexican, came in at 56.69 kg.
BURGOS STOPS ARCHULETA
In the other big fight on the bill, Juan Carlos Burgos beat Frankie Archuleta in the second round of a featherweight contest.
Archuleta, 35, was down three times in the second round before referee Gerald Ritter stopped the action at 2 minutes 33 seconds.
Burgos, who ranked No 4 by the WBC, improved his record to 26-1, with 19 knockouts. Archuleta dropped to 27-8-1; 14. The bout was at a weight limit of 58 kg.
The tournament was presented jointly by Art Pelullo/Banner Promotions, Golden Gloves Promotions, Thompson Boxing Promotions and Tony Holden Productions.
In Palm Bay, Florida, Jesus Pabon stopped Americo Santos in the first round to take the vacant WBO Latino junior welterweight title.
Santos was down twice before the bout was stopped 2 minutes 45 second into the opening round. Pabon now stands at 17-1; 11 and Santos dropped to 26-4-1, 22.