Brooklyn mechanic turned a court witness box into a sound stage Monday as he belted out an oldies tune he claims got him wrongfully arrested in 2013.

Mark Holt sued the city, claiming MTA cop Jose Deras handcuffed him inside the Atlantic Terminal subway station for singing the Spinners tune “Smile, We Have Each Other,’’ Brooklyn federal court papers state.

Holt told jurors he performed the rendition to comfort a friend.