Nicknamed "El Brujo," or "The Wizard," for his ability to fool hitters, the Enea, Los Santos, native has his sights set on pitching for Panama and helping it qualify for the main tournament, set for March 2013.
"It's a source of pride for me," said Mendoza at the end of his first day of training. "It's a great honor to wear Panama's uniform. I want to do it here, in front of my fans and I hope it's not the last time.
Mendoza played 10 seasons in the Major Leagues with the Yankees and Red Sox, from 1996 to 2005.
The former World Series champion, who had a 59-40 record in the Mayors, completed an exhausting week of training with the Panamanian squad.
"It's been a long time since I trained like this. The sun was pretty intense, but we're getting ready for this pace," said Mendoza.
Panama is training at the Jose Antonio Ramon Cantera Stadium in the city of Aguadulce, where three standout big leaguers were born: Carlos Lee, left-hander David Romero and Juan Berenguer.
Panama will face Brazil on Nov. 15 in the first game of the qualifying round at Rod Carew Stadium, which has a capacity of 27,500 and is being remodeled.
"It is a wonderful experience," said Mendoza. "I [am coming] to do my part to help the boys, but I know they have a lot to offer for Panama."
During the elimination round, Panama will compete for a berth in the 2013 World Baseball Classic against teams made up of the best players from Colombia, Brazil and Nicaragua.
The last time Mendoza pitched in the big leagues was in 2005 with Boston. At age 40, he continues to train like a youngster -- and the only thing on his mind is contributing wisdom and quality when he takes the mound.
"I want to wear number 55, and I will fight to get it," said Mendoza.
Panama had no victories in the first two World Baseball Classics in 2006 and 2009.
Jose Pineda is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.