I did not play my best so that he could win

[navi tasan]

1-I did not play my best so that the child could beat me.
2-I did not play my best, so that the child could beat me.

3-I did not play my best for the child to beat me.
4-I did not play my best, for the child to beat me.

5-I did not play my best in order for the child to beat me.
6-I did not play my best, in order for the child to beat me.

Are these sentences correct?
They are all supposed to mean:
For the child to beat me, I did not play my best.
My intention was for the child to beat me and that is why I did not play my best.

It seems to me that the comma is option in the first pair but necessary in the other two pairs.

[5jj]

1-I did not play my best so that the child could beat me.
2-I did not play my best, so that the child could beat me.

Neither of these is clear; they could be interpreted as 'I did not play my best, with the result that the child was able able to beat me'. #1 could also be interpreted as "The reason for my not playing my best was not to allow the child to beat me (but ...). Your meaning is clear if you change the order of the clauses in #2: 'So that the child could beat me, I did not play my best'.

3-I did not play my best for the child to beat me.
4-I did not play my best, for the child to beat me.

Neither of these is natural, or clear, in my opinion.

5-I did not play my best in order for the child to beat me.
6-I did not play my best, in order for the child to beat me.

#6 is better with the order changed: "In order for the child to beat me, I did not play my best.

5

[SoothingDave]

"I let him win" is pretty straightforward way of expressing this.