Lamont Peterson has lodged an appeal against the WBA's decision to order a rematch against Amir Khan.
The governing body last week sanctioned a repeat of the light-welterweight bout after Peterson won in controversial circumstances on 10 December.
But the 27-year-old American, who will keep the IBF version of the title after Khan withdrew an appeal over the result, is contesting the judgment.
"We are confident the WBA will overturn its decision," Peterson's camp said.
In a written appeal they also asked the WBA to "recognise Lamont Peterson as the true and final WBA light-welterweight world champion."
Khan, 25, responded on Twitter by saying: "Now I've heard Peterson is appealing against the WBA ruling a rematch. He said he was going to give me a rematch after the fight so why go against it?"
Peterson's advisers claim Khan withdrew his appeal to the IBF because his case did not stand up, although Khan's camp said their issue was that "only partial representation of fight officials who were involved" in the initial fight would be present.
Khan's team appealed to have the points loss in Washington DC overturned after concerns over referee Joseph Cooper and the judging of the fight.
"Mystery man" Mustafa Ameen was at the centre of Khan's questioning after he appeared to interfere with the scoring by WBA supervisor Michael Welsh during the fight.
But Ameen told BBC Sport in an exclusive interview that he was correcting errors made by Welsh, who had said he was unwell.
"I noticed one error and a subsequent error. I assisted him in correcting it without touching anything," he said.
Richard Schaefer, chief executive of Khan's promoter Golden Boy, responded by saying: "Ameen's explanation doesn't really sound plausible.
"Welsh seemed perfectly capable of adding a scoresheet."
Khan's camp, which has offered a rematch to Peterson on 19 May in Los Angeles, was granted an immediate rematch by the World Boxing Association last week because of "multiple irregularities" in December's controversial fight.
But Peterson refuted claims talks for a rematch were ongoing between the two parties.
And Peterson's trainer, manager and mentor Barry Hunter said: "We are extremely pleased that Golden Boy and Amir Khan withdrew their protest with the IBF.
"The Peterson team continuously responded to each of Khan's accusations and the absurdity of the claims. Our reply addressed the rules and also Khan's inability to make adjustments and his performance in the ring, as opposed to placing blame on almost everyone associated with the bout."
Peterson added: "Now that this is over I am ready to move on. As I said before, as champion I plan on representing both sanctioning bodies to the best of ability and that means fighting the best fighters in the world in defending my titles."
Ameen denies any allegations of wrongdoing during the original bout, and has demanded an apology from Khan and his camp.
He insists his only intervention was to correct Welsh's maths after he erroneously calculated the scores for the first three rounds.
"I happened to look down, I believe at the end of the third round, I looked down and I saw Mr Welsh's score," he added.
"I saw, I believe, it could have been nine, nine and nine - which is 27 all day long. There was an error. It might have been 26 or 28 but he was off by a point or two.
"I happened to look down and I said 'Michael, nine times three is 27'. He said 'oh my God' and corrected himself.
"And he said 'I'm not feeling well this evening, thank you very much'."
Khan's camp also questioned why Ameen was pictured with Peterson in the ring after the fight.
But Ameen said he was assisting 85-year-old IBF official Paul Artiist with the championship belt and insisted he would have done the same had Khan won.
Welsh declined to comment and directed all questions to the WBA.
Olympic silver medallist Khan lost his titles after he was deducted a point in two rounds by referee Cooper for pushing his opponent.
Judges George Hill and Valerie Dorsett scored the fight 113-112 to Peterson, while Nelson Vasquez gave the verdict to Khan 115-110.