Twelve months of steadily simmering acrimony reaches boiling point here Saturday when world middleweight king Gennady Golovkin faces off against Saul "Canelo" Alvarez in their long-awaited Las Vegas rematch.
Golovkin, the unbeaten WBA, WBC and IBO champion, will be chasing a place in boxing history as he attempts to make a record-breaking 21st consecutive defense of his middleweight crowns against Mexican idol Alvarez at a sold-out T-Mobile Arena.
But the Kazakh champion's tilt at the record books has become a footnote in a build-up dominated by the furor that erupted when Alvarez failed two drug tests in February, scuppering a planned May 5 rematch.
Alvarez, who was later suspended for six months by the Nevada State Athletic Commission, insists the banned substance - Clenbuterol - entered his system via contaminated meat in his native Mexico.
Golovkin, who most observers believe should have been awarded victory in last September's drawn first fight, has rubbished Alvarez's explanation for the failed drug tests.
The 2004 Olympic silver medallist, (38-0-1, 34 knockouts), has repeatedly accused his Mexican opponent of doping, raising the temperature in Las Vegas this week by voicing his suspicions again.
"These stories about contaminated meat are nonsense," Golovkin said, claiming to have seen injection marks on Alvarez's body in photos of his opponent.
"You couldn't deny there was some injection marks on his hands and his arms. Injection marks were evidently there," Golovkin said.
"Everywhere, biceps, stomach, pretty much all over his body you could see injection marks."
For the most part, the animosity between the two men has had a ring of authenticity about it.
Alvarez, whose only defeat in a 52-fight career was a 2013 loss to Floyd Mayweather, admits the accusations have riled him.