bending the knees is the key here. if it is a very low slice, you also need to swing very fast to get the ball over the net to counter the ball's backspin.
It is not an easy shot. On a good day, you can do it, but what about most of the time when you are not above your normal form. so you should complement it with the slice. when the ball is so low and fast that there is even no space for you to place your racket below the ball, a slice a safe shot to keep it in play.