Rating Calculation Q.

let's imagine a player (x) who's rating is 1800 played against a player (y) who's rating is 1850 .

If (x) won the first match and lost the second match against (y) , is it equal to a one drawn game between them in terms of rating change?

and is there a difference if (x) won the first and lost the second and the reverse situation which is (x) lost the first and won the second in terms of change in rating !

 

There is indeed a difference in rating outcome between the two scenarios.

The reason behind that is quite straightforward. While in the initial situation the difference between the two players is 50 Elo, the second game will result in a lower/higher rating gain for the winner if their first game was decisive.

For Example: Let's assume "Player Y (1850) vs. Player X (1800)" results in a win for white and Player Y gains 17 Pts. due to that win.

In the following game "Player X (1783) vs. Player Y (1867)", Player X wins and gains a number of Elo points > 17 (e.g. 20 Pts.), since the rating difference between them is now greater than 50 Pts.

[Player X (1803) / Player Y (1847) - in our example]

Therefore, it is always better to win your last game =)

Thanks @Mila_Kunis 

and is the final result (1803/1847) of the two games is equivalent to a 1 game which ended in a draw or not ? if yes which of the two scenarios is closer to a draw :D I feel confused about this 

Pretty sure chess.com uses your current rating.

For example if you started a daily game with someone and your rating was 1200, then a month later the game ends and your rating is 1300, the calculation is done with your 1300 rating.