Terrence Howard -- Calls Witness who Says Threesome Sex Tape Used for Extortion

Terrence Howard squared off in court this morning with ex-wife Michelle Ghent ... and the first witness was the actor's sister-in-law, whose testimony was read out loud, about a threesome sex tape that was allegedly used to extort Howard out of money.

Terrence is trying to get the divorce settlement thrown out on grounds he signed it under duress, claiming Michelle held sex tapes and photos over his head in order to get way more support than she was entitled to receive. She got $5,800 a month for 3 years, even though they were only married for a year.

Yvonne Howard, Terrence's sister-in-law, testified Michelle said she "had him [Terrence] by the balls," and then claimed to have a tape where Terrence is having sex with a woman and another woman is present. It's odd it's called a threesome, because the testimony only referred to one female engaged with Terrence. The other female was filming.

On his way out during the lunch break, Terrence said wants justice to prevail ... and then plugged Mariah Carey on "Empire."