WBC flyweight champion Julio Cesar Martinez moves up to 115lbs to take on the legendary Roman Gonzalez in San Diego in the early hours of Sunday morning.
Gonzalez was due to be facing Juan Francisco Estrada in a highly-anticipated trilogy fight, but Estrada was forced to pull out of the contest. Chocolatito is 4/6 to beat his Mexican opponent, who has taken the fight at short-notice and faces his first real test at super-flyweight.
Martinez is 6/5 to win what should be a fantastic fight and the draw is available at 16/1.
Gonzalez is 21/10 win by stoppage and 12/5 to triumph on points, while El Rey is 4/1 for a knockout victory, 5/2 for a decision win and the bout is 8/11 to go the full 12 rounds.
Here's everything you need to know ahead of the fight.
The bout will take place at the Pechanga Arena in San Diego. The fighters are expected to get it on at around 1.30am UK time on Sunday.
The contest will be shown live in over 200 countries on streaming service DAZN.
Gonzalez is a legendary fighter and he has contested 53 professional bouts in a career that started in 2005. Chocolatito has tasted defeat on just three occasions, once to Estrada and twice against Srisaket Sor Rungvisai.
The Nicaraguan boxer has won world titles in four different weight classes, having been crowned champion at minimumweight, light-flyweight, flyweight, and super-flyweight.
Chocolatito has 41 knockout victories on his card and his only stoppage defeat came in his second fight against Rungvisai.
Martinez has just a single loss on his professional record and that came in his very first bout. El Rey has since won 18 fights and he has been involved in two no contestes against Charlie Edwards and McWilliams Arroyo.
The 27-year-old captured the vacant WBC flyweight belt when stopping Cristofer Rosales in 2019.
El Rey has seen 14 of his 18 victories come by stoppage, but he was knocked down himself in that no contest against Arroyo.
There are no titles up for grabs in San Diego, but Martinez could look to a unification fight against Edwards back down at 112lbs, if he comes through against Gonzalez.
This looks a tough bout to call in terms of the winner, but it should be a terrific tussle. This bout was hastily arranged, after Estrada's withdrawal, and Martinez has agreed to make the step-up to 115lbs.
Clearly, there have to be question marks over El Rey at super-flyweight, but Martinez is seven years younger than his 34-year-old opponent.
Chocolatito is a brilliant boxer and his aggressive style often makes for great viewing. The Nicaraguan will look to pressure Martinez and it's unlikely that El Rey will want to give up the center of the ring.
When you consider the fighting style of these boxers, and the fact it takes place at 115lb, it may not be as likely to go the distance at the prices suggest. Both boxers carry plenty of power and they will come to the ring with a little more bulk at super-flyweight.
This is a fight well worth watching and backing it not to go the distance at 1/1 looks a decent bet.