Tic-Tac-Toe

The game of Tic-Tac-Toe is  played in a large square divided into nine small squares. 

[1] Each of two players in turn places his or her mark – usually X or O _ in a small square. 
[2] The player who first gets three marks in a horizontal, vertical and diagonal line wins. 
[3] A player will always place his or her mark in a line that already contains (a) two of his or her own marks or (b) two of his or her opponent’s marks – giving (a) priority over (b)

Assume that both the players are intelligent enough.

1. Who will win the game, O or X?

2. Which was the sixth mark and at which position?

Source : The great book of Puzzles and Teasers 

See our previous ‘Puzzles of the Day’:

Puzzle of the Day : 35

Puzzle of the Day : 34