Do it in Normal Difficulty.
In Easy difficulty the computer tends to make random moves which make the game go longer.
All i did is go really fast and click fastest possible anywhere and not really try a strategy at first to put as much X on the board in the fastest time. Then when you have at least 2 X in 5 of the 9 boards use more strategy to win fast.
Took me less than 10 games to do and i'm not that good at that game.