The best tennis player in the world is no match for Jimmy Butler -- the NBA superstar proved he's got serious skills on more courts than just the hardwood ... by scoring a point off Carlos Alcaraz during a U.S. Open charity event!!
The Miami Heat hooper was serving as an honorary ball boy for the Spanish star's contest against Frances Tiafoe at the Stars of the Open at Louis Armstrong Stadium on Wednesday ... when all of a sudden, he decided to step in and show off his tennis game.