Bernard Hopkins beat Tavoris Cloud to break his own record as the oldest world champion in boxing history.
The 48-year-old American claimed the IBF light-heavyweight crown with a unanimous points win in New York City.
Hopkins, who has been linked as a possible future opponent of Wales' Nathan Cleverly, took full advantage of cutting 31-year-old Cloud above his right eye in the sixth round.
Veteran Hopkins first became the oldest world champion with a May 2011 victory.
The decisive sixth-round moment was ruled by the referee to have been an accidental clash of heads but replays showed the damage was done by a left hook.
The judges awarded the fight to former undisputed world middleweight champion Hopkins by scores of 117-111, 116-112, and 116-112.
Hopkins, who now has 53 wins from 61 fights, made headlines nearly two years ago when he defeated Canada's Jean Pascal for the WBC light-heavyweight title.
When he was comfortably beaten by Chad Dawson last April, many thought he would finally announce his retirement.
But his latest victory, to the delight of the majority of the crowd at the Barclays Center, again rewrote the history books.