Chaka Khan Duets with Stevie Wonder for Her 70th Birthday, Icons Pack Party

Chaka Khan's celebrating her 70th birthday, and she can still turn up like her heyday in the '70s and '80s ... and she did with an assist from fellow icon, Stevie Wonder!

Chaka held court for her celebration Thursday night at Vortex recording studio in Hollywood, partying with a couple hundred guests who joined Stevie in singing happy birthday -- his version, of course.

Once Stevie got behind the keyboard the party was in full swing -- he and Chaka did her hit, "Tell Me Something Good" ... and then they belted out one of his Motown classics, "Signed, Sealed, Delivered."

Looks like Mr. Wonder worked up quite the appetite during the festivities ... we hear from folks inside the event, he brought in Chick-fil-A for his entourage, which he definitely enjoyed.

Joni Mitchell's another legend who came out to honor Chaka ... along with comedian Mike Epps, and later in the night Tiffany Haddish jumped on stage too.

Tiff got the band fired up to play "Proud Mary," as she belted out the lyrics and even attempted some of Tina Turner's moves.