Shannon Briggs scored a sensational last-second knockout victory against Serguei Lyakhovich to take the WBO heavyweight title in Phoenix.
Briggs left it late before securing his first world title
Briggs trailed on all three judges' scorecards entering the 12th round but punched the champion through the ropes to win a world crown at the age of 34.
"I was tired," he admitted. "I used a lot of energy in the first round trying to get him out. I almost blew it.
"I would've probably gone home and shot myself in the head if I hadn't won."
Lyakhovich, born in Belarus but now a US citizen, said: "I didn't fight my fight. I fought his fight.
"It just didn't happen. I took his best shot. He caught me right on the chin. It was just a lack of punches before. I wasn't right there."
Until Briggs's win, all four major heavyweight titles were in the hands of boxers from former Soviet Union states.
We want Klitschko, we want Maskaev. We want them all until we unify the crown
Russian giant Nikolay Valuev owns the WBA crown, Kazak-born Oleg Maskaev owns the WBC belt and Ukraine's Wladimir Klitschko the IBF title.
Spectators booed the fighters through most of the bout, which progressed at a tedious pace.
Behind on points, Briggs needed a big final round and sent Lyakhovich to the canvas with 30 seconds remaining.
He got to his feet but backed up against the ropes as Briggs launched one more frantic assault.
The American handed two body blows to double over Lyakhovich, who then fell backwards between the ropes.
Lyakhovich lay sprawled on his back on a ringside table, his head landing next to the bell, his reign over.
Briggs, 35 next month, last fought for a world title eight years ago when he faced Britain's Lennox Lewis for the WBC belt and was stopped in five rounds.
The only longer fight in his career was his 12-round triumph over George Foreman in 1997.
Only twice before had Lyakhovich gone past the 10th round, most recently in a 12-round decision in April over Lamon Brewster to take the WBO title.
Briggs improved to 48-4 with one draw by winning his 42nd victory inside the distance. It was his 12th triumph in a row over the past four-and-a-half years.
Lyakhovich, who fell to 23-2, led on two judges' cards by 106-103 and the other by 105-104 before his last-gasp defeat.
On the undercard, unbeaten WBA lightweight champion Juan Diaz scored a unanimous 118-109, 118-109, 116-111 points win over Fernando Angulo to keep his title.
In his first fight since his loss to Britain's Ricky Hatton, former WBA welterweight champion Luis Collazo stopped Artur Atadzhanov in round six.