Down in Miami, Marlins centerfielder Jazz Chisholm Jr. held nothing back for his team's Thursday matinee against the Mets ... sporting some loud, orange camo pants. His teammate, Luis Arraez, went with a more muted look, wearing a simple, button-down shirt.

In the opposing locker room, New York star Pete Alonso brought out a pair of flashy pants of his own -- while making sure his belt buckle -- and his mustache!! -- were the stars of his 'fit.

Blue Jays pitcher Alek Manoah, meanwhile, broke out a classic Sandlot jersey for Toronto's opener ... one that featured all of the guys from the iconic movie, including Hamilton "The Babe" Porter. Manoah was also dripped out in some dark shades and a maple leaf chain.

In the Bronx, San Francisco Giants closer Camilo Doval made The Big Apple look like The Wild West ... arriving with a huge cowboy hat on his head. Giants pitcher Logan Webb chose to pay homage to Dennis Rodman with his attire.

Other players opted for a more laid-back approach to the season opener -- with Tigers stars Javier Báez and Eduardo Rodriguez wearing some casual shirts and jeans.