Nathan Cleverly's unbeaten record was ended by Russian Sergey Kovalev, who took the Welshman's WBO light-heavyweight world title with a fourth-round stoppage in Cardiff.
The 26-year-old Cleverly had been seeking headline unification fights in America and was under pressure to impress an American audience with his sixth defence at the Motorpoint Arena being televised across the Atlantic.
However, Kovalev tore up the script in the Welsh capital by flooring Cleverly twice in the third round and forcing a stoppage in the next session to disappoint the thousands of Cleverly fans and take the title.
America-based Kovalev, 30, went into the fight with a 21-0-1 record and already has a following in the United States with many fancying him to snatch Cleverly's world title in the Cefn Fforest man's backyard.
The challenger was looking to land big right hands from the first minute and won the opening round quite clearly.
Cleverly was busy but made few inroads, despite somehow opening a cut over the challenger's right eye. Kovalev, meanwhile, was successfully deploying the jab followed by a driven right hand on a regular basis.
Cleverly landed a decent back hand of his own towards the end of the second which was his only real moment of success up to that point.
Cleverly was rocked badly by a left and went down moments later from a clubbing right. He rose to his feet but was unsteady and moments later he was down from another right to the head, made worse by Kovalev hitting him again as he sank to one knee.
He was out on his feet again and referee Terry O'Connor was poised to stop it, only for the bell to save the Briton.
Kovalev went for it in the fourth and unleashed as many power shots as he could muster. A right and hooking left sent Cleverly wobbly again 29 seconds into the round and O'Connor this time decided enough was enough.
Cleverly's record now reads 26-1 (12 KO wins) while fearsome Kovalev moves to 22-0-1 (20KOs).
On the undercard, Liverpool's Stephen Smith stopped Gary Buckland with a seething short right uppercut in the fifth to leave the Welsh champion out cold and win the British super-featherweight title.
Swansea favourite Enzo Maccarinelli won the Commonwealth light-heavyweight belt from Ovill McKenzie with an uppercut of his own in the 11th round to inject new life into his career.