Maria Sharapova's lawyer, John Haggerty, says the Court of Arbitration's (CAS) ruling to lower her doping ban from two years to 15 months is a "stunning repudiation" of the International Tennis Federation (ITF).
The five-time grand slam champion admitted to taking the banned substance meldonium after testing positive at this year's Australian Open and was originally due to be suspended until January 2018.
However, Sharapova maintained that she was unaware the drug had been added to the World Anti-Doping Agency's list of prohibited substances, and CAS announced it has reduced her penalty on Tuesday.
Haggerty labelled the ITF's original decision as "pure fiction" and hit out at the governing body's handling of the situation.
In a lengthy statement, Haggerty wrote: "The CAS decision is a stunning repudiation of the ITF and it exposes the ITF decision for what it is: Pure Fiction. It shows that what you really have here is an honest administrative mistake that Maria took responsibility for from the very start.
"She did not double check with her agent to be sure no rule changes had gone into effect on January 1st. And that's why over a 26-day period in January, she continued to take three over-the-counter supplements that she had been legally taking for the preceding 10 years.
"CAS striking down the ITF ruling is another in a growing list of cases where CAS has determined that the ITF Tribunal's decision was wrong. In fact, the last time CAS upheld an ITF ruling was way back in 2009.
"Clearly, the ITF Tribunals are wrong far too often. And the really sad part about that here is Maria was forced to live with the ITF's bad judgment and faulty conclusions for many months. Hopefully, this CAS decision will be a wake-up call to future ITF Tribunals.
"In many sports, an athlete who deliberately cheats gets suspended for about a third of a season. CAS has made clear that Maria made an honest mistake, and for that she has been suspended for one and 1/4 seasons.
"The system is flawed when the rules require a 15-month suspension for an honest mistake. I am very glad Maria's suspension has been substantially reduced and that she will be back playing tennis in April.
"I am equally glad that the express language of the CAS decision forever lays to rest the fiction that was the ITF Tribunal decision. The ITF handled this matter poorly from start to finish.
"Maria took responsibility for her mistake. It's time for the ITF to take responsibility for its mistakes and change its procedures so that this can never happen to another player. Based on this ruling, the ITF has a lot to learn."
Haggerty added: "I have never seen a ruling like this before. I have seen reductions in suspensions before - although I will say a nine-month reduction is one of the longer reductions I have seen.
"As we demonstrated before CAS, not only did the tennis anti-doping authorities fail to properly warn Maria, if you compare what the ITF did with how other Federations warned athletes of the rule change, it's a night and day difference.
"The tennis anti-doping authorities let Maria down."