Derren Brown plays chess with nine professional chess players simultaneously – and beats more than half of them! He then explains the techniques he used to achieve this stunning effect, as you can see in this video.
But how did he predict the exact number of pieces left on the boards?
He didn't. He simply wrote the numbers down after the games had already been finished. He then used some sleight of hand to force the paper with the right numbers into grandmaster's hands.
You can see him doing this on the video right before they reveal the numbers. We cannot see exactly what he is doing, but there is definitely something going on.