Vocal troupe Afro-Blue solidified their place as our favorite contestants on this season of NBC's The Sing-Off earlier this week with two more stellar, just-crown-them-the-winners-already performances. The jazz group had to switch gears and come out of their comfort zone a tad when asked to perform a current radio hit for their first selection. After stating that "Afro-Blue does not perform pop songs at all" in their pre-performance video, I was on the edge of my seat when they started singing Estelle's "American Boy." Any fears were instantly quelled, however, when different members of the expertly color-coordinated ensemble started scatting, beat-boxing, and harmonizing. They were in a zone, taking Estelle's song to unheard of heights with their original arrangement. Once again, the judges agreed that they were the cat's meow, but some criticism came later in the show after Afro-Blue performed Marvin Gaye's "I Heard It Through the Grapevine" for their '60s classic selection. Admittedly not as strong as their first song, it seemed to me that the judges were a little nit-picky in their critiques. Nonetheless, the judges did get it right when they advanced Afro-Blue on to the next round at the end of the episode. If you missed them on Monday night, watch them in action below and after the bounce, and see why they are the ones to beat -- which will be very, very hard.