Sam disappeared from the chess board.
While the Mountain Master fainted as he entered one of the special spaces in the void where the trio brought the three young masters. Sam didn't go there of course.
As for how it is possible now, from outside to that space, Sam's cultivation level and the mountain master's level are worlds apart, but from the board to the space, their levels are same. Sam didn't know whether it would work out or not.
But luckily it did.
The Mountain Master stayed there unconscious for fifteen minutes before coming to himself. He was shocked at the start and didn't know where he was and why he was there.
But after some time, everything came back to him. He looked around trying to find a way out.
Meanwhile, Sam reappeared back at their gathering point.
"So, how did the battle go?"
That is the first thing that they asked as soon as he came.