Now that his Minnesota Timberwolves have gon' fishin' ... the NBA superstar took his talents back to Chicago where he decided to put his singing skills on display at PRYSM Nightclub.

The song? "Let Me Love You" by Mario ... and Butler didn't sound too bad!

In fact, the crowd loved it -- especially one female fan who got onstage and started dancing it out with the 28-year-old.

For the record, the headline performer that night was T-Pain ... but Jimmy Buckets stole the show!

We're told Jimmy's performance was totally random and unplanned -- and went down around 2:30 AM.

Of course, Jimmy's a fan favorite in Chicago after killing it with the Bulls for a few seasons.

Nice to see he's still getting love.