A green ball was positioned over the corner pocket, which the cue ball narrowly passed after bouncing off of the far end cushion.
As the cue ball bounced off to the left, the yellow cannoned into the black ball which then moved in the same direction.
However, the cue ball was positioned right up against the table cushion, making the shot difficult.
The Welsh cueist smiled in disbelief at the shot, while the referee was also visibly stunned as he pursed his lips.
Stevens did go on to win the frame 76-39 before restoring his two-frame advantage by winning frame four 113-1.
