Randall Bailey stunned Mike Jones with an 11th-round knockout to claim the IBF welterweight title in Las Vegas on Saturday.
Bailey, a former light welterweight champion but now in his 38th year, was expected to give the unbeaten Jones his biggest test yet.
In a classic boxer versus puncher match-up, Jones did what he does best, fighting in bursts before nipping out of range.
But Bailey caught up with him in the 10th, landing a hard right hand to drop Jones for the first time in his career.
The veteran could taste blood, and an explosive right upper cut sent the American to the floor once again in the next, and this time Jones was out cold.
Bailey could now face the winner of the Kell Brook v Carson Jones fight on July 7.
On a big night at the MGM Grand, former two-time Olympic champion Guillermo Rigondeaux successfully defended his WBA super-bantamweight title against Teon Kennedy.
Rigondeaux moved to 10-0 in impressive fashion, dropping Kennedy no fewer than five times with the left hand doing most of the damage.
When a quick combination floored Kennedy again in the fifth round, referee Russell Mora waved the fight off.