Yasiel Puig -- Hits 1st Home Run ... Then Hits the Clubs!

Seems the "old" Yasiel Puig is finally coming back ... 'cause after a quiet, slumping, terrible start to the MLB season ... Puig hit his 1st home run of the year yesterday -- and then he hit the clubs!

The 24-year-old star partied at Greystone Manor in West Hollywood late Sunday night ... hours after his 1-5 performance helped the Dodgers defeat the Arizona Diamondbacks.

Puig is in a pretty nasty slump this season -- he's only 3 for 22 with a .136 average ... not ideal for a guy in a $42 million contract.

In the past, Puig's been a staple on the club scene -- and Dodgers owner Magic Johnson has said that he's totally cool with it as long as the team wins.