Lee Selby put Ricky Burns' career in doubt as he edged a hard-fought contest between the two former world champions at London's O2 Arena.
The judges gave the Barry fighter the nod in the lightweight bout, scoring it 115-115, 116-112, 116-113.
In his first fight in almost a year, 36-year-old Burns looked strong but Selby's desire and quick reflexes kept him coming forward.
Selby can now target Ukraine's Vasiliy Lomachenko.
The Coatbridge fighter controlled the middle of the ring in the early rounds but found Selby's lateral movement and quick fists a challenge. However, most of the Welshman's assaults hit Burns' gloves.
- Live: Super Series Final - Prograis v Taylor
- 'No way back for loser' - Selby
- Chisora stops Price in fourth round
It was a contest Selby claimed beforehand: "There is a lot on the line in this one, it could be career-defining, you could say."
Having dropped from the 140lb division and with Selby having moved up from lightweight, where he held the IBF world title, Burns' punches looked the more telling.
A right hook to Selby's ribs in the third round and a trio of downward clubbing right hands in the fourth were his best shots at that point.
The pair had shown respect for the other's achievements in the sport in the fight build-up and that was evident in the opening exchanges.
However, at the end of the fifth, Burns gestured to the referee and looked angry as he struck his opponent after the bell, sparking a furious reaction in Selby's corner.
The former sparring partners were brought together three times for a talking to by referee Bob Williams in the middle rounds as Burns tried to land the heftier hits against a quick-fire-witted opponent.
Selby, though, looked focused and unhurt as the bout moved in to the final third. He caught the Scot with a big overhead right in the eighth and a flurry of punches soon after. The smile this drew from Burns was wiped off his face by a left hook to his jaw after the bell.
The Barry fighter had survived bad cuts to his eyes in his two fights since losing his IBF world featherweight title to Josh Warrington in Leeds in May 2018.
That grit was evident as the fight reached its climax, thumping a right hand into Burns' face in the 11th as the Scot, in his 52nd bout, increasingly tried to tie him up in clinches.
The final round typified the fight, with both showing tremendous heart and it was Selby whose arm was raised in a split decision.