Britain's Lewis Ritson claimed an unconvincing split-decision points win over Mexico's Miguel Vazquez to take the vacant WBA intercontinental light-welterweight title in Peterborough.
Two judges scored the contest 117-111 and 115-113 in favour of Ritson, while the other gave it to Vazquez 116-113.
"I think I was getting the clearer shots," Ritson told Sky Sports. "I was confident that I won the fight."
But Ritson's promoter Eddie Hearn thought Vazquez deserved to win.
A post-fight tweet from Hearn, who did not attend the bout because of coronavirus restrictions, read: "Watching from home and felt Vazquez deserved the win there."
Others in the British boxing community were incensed by the decision.
Manager Sam Jones - who guides the career of British heavyweight Joe Joyce - tweeted: "I promise that's the worst decision I've ever seen in boxing."
And boxing trainer Dave Coldwell wrote: "Spoilt a great show for me there. Upsets, great fights all the way through and then you get an absolutely scandalous decision that takes the headlines and conversations away from all the good adverts for our sport from the rest of the bill."
Newcastle fighter Ritson, 27, has now won 21 of his 22 bouts as a professional.