Play video content EXCLUSIVE

This is adorably hilarious ... Washington Nats 2B Danny Espinosa TRYING to do one of those "gender reveals" with a pinata and a baseball bat -- but his big league swing betrayed him!

Espinosa's wife Sara was filming the event ... in which he was supposed to obliterate the pinata, thus revealing the sex of the baby to the world (you've all see stuff like this on your Facebook feed).

What happened next ... well, let's just say "curveball."

FYI -- He WAS able to make contact after he ran the count full ... verdict? It's a boy! (See pics below).