Roy Jones Jr. believes Vasiliy Lomachenko made a fatal mistake that cost him in his fight with Devin Haney.

Lomachenko challenged for Haney's lightweight titles last month in an extremely close and competitive contest that saw the champion come out on top by points with the three judges scoring it 116-112, 115-113 and 115-113.

It was a decision that didn't go down well with the crowd, boxing fans, fellow fighters or Lomachenko's team as many felt the Ukrainian did more than enough to become the new undisputed lightweight champion.

Lomachenko was so sure he had won that he even revealed he took the 12th and final round off.

“[I thought] maybe I can give him this round,” he said at the post-fight press conference. “I don’t need to win this round because I was winning the other 11 rounds. I don’t say every round but during the rounds, it was mine.

“I don’t know, maybe I don’t understand boxing.”

For Jones Jr., this was a pivotal mistake by Lomachenko as had the latter not taken the final round off, he could have still salvaged a draw at the very least even with the judges' scorecards.

“Everybody got so mad about the Haney decision,” Jones told Fight Hub TV (via Boxing Social). “For me, if you’re not the champion, why are you giving him a round off? You take round 12, the last round, off? You don’t give no round off. You not the champ, he is!

“And guess what, had you won that round, you would’ve had a draw across the draw. Had you got a two-point round that round, you’d have won the fight clearly. Come on, bruh. It’s not rocket science. As hard as he pushed you at that weigh-in, and you gave him a round off? Come on. Lomachenko is one of my favourites, but you can’t take a round off when you’re in championship boxing and you fight a man for his belts.”

As far as his own scorecard went, Jones Jr. refused to state Haney beat Lomachenko. But at the same time, he feels the American deserved to keep his belts.

“In my opinion, [Haney] deserved to keep his title. I ain’t gonna say he beat him, because I thought they both did good in the fight,” he added. “It could go either way, but in a fight that close they’re gonna leave the champ the champ. To take the belt from the champ you gotta dominate the champ.”