WBA lightweight champion Juan Diaz scored a technical knockout over Acelino Freitas after eight rounds of their unification bout in Connecticut.
Juan Diaz has held his world title since July 2004
The Mexican, 23, won when Freitas, a four-time world champion and the WBO title-holder, failed to leave his corner at the start of the ninth round.
Diaz raised his record to 32-0, with 16 of the wins by knockout. It was his sixth defence of the WBA belt.
"He's a tough guy, a true warrior," Diaz said of Brazil's Freitas (38-2).
In Oberhausen, Germany, WBA middleweight champion Felix Sturm gained revenge over Spain's Javier Castillejo with a unanimous points win.
Castillejo (62-7, 41 KOs) caused an upset last July when he took the German's title with a 10th round stoppage after which Sturm was taken to hospital with a suspected broken jaw.
This time, Sturm boxed cleverly and refused to be drawn into an out-and-out brawl, with the judges ruling the fight 116-112, 115-114 and 116-112.
"I think I showed I learned from my mistake - it's better to fight with your head," said Sturm (27-2, 12 KOs) . "I think I can stay champion a long time this time."
On the same bill, Croatia's Stipe Drews became the new WBA light heavyweight champion with unanimous points victory over Silvio Branco of Italy.
Drews (32-1, 13 KOs) also beat Branco (55-9-2, 34 KOs) in a fight for the European title three years ago.
In Atlantico, Colombia, Ivan Calderon defended his WBO strawweight title with a split-decision points win over Ronald Barrera. Ricardo Torres retained his WBO light welterweight crown with a unanimous points decision over Arturo Morua.