Alex Rodriguez says the Mets are going to be SUPER HAPPY with their new manager, Carlos Beltran ... telling TMZ Sports he thinks the guy is "a baseball savant."
"The Mets are going to love him," A-Rod says.
New York has stumbled the last few years with Mickey Callaway and Terry Collins running the dugout ... but Rodriguez seems convinced 42-year-old Beltran will turn things around next year.
Of course, A-Rod is a bit biased -- dude played with Carlos for a few years with the Yankees earlier this decade -- but he swears the ex-outfielder will kill it with the Mets.