Which sentence is correct? Kindly give an explanation.?

With the addition of a comma, either could be correct.

Assuming* (see update) that 'Wesley So' is the person's name, each sentence requires a comma after "So". Then, either sentence could be correct, depending on context:

Sentence 1 is correct if congratulating Wesley So because he DID win the event, which is now finished.

Sentence 2 could be correct if the event has not yet been completed, and although the speaker doesn't expect Wesley to win, we're congratulating him for participating, or for his contributions to the event, etc.

*UPDATE: I now understand that Wesley So is a Filipino-American chess grandmaster.

Neither is correct because "so as" doesn't make any sense.

Correct: Kudos to Wesley. I did not expect him to win this blitz event.

First sentence, with a comma after the name "Wesley So."

Eliminate "So" and use "did" because he has already won and that makes "do" wrong. It should be: Kudos to Wesley as I did not expect him to win this blitz event.

presumably you are praising Mr So for having already won, so you must use past tense and say that you did not expect him to win (and found out that your expectations were wrong). It is possible that you do not expect him to win and he hasn't competed yet so you don't know if he will win, or not, but then it raises the question as to why you are praising him when nothing praise-worthy has been achieved (yet).

If you omit "so" the first is correct.

The first sentence

But please put a comma after So.

the first one is correct sentence. Although he won this thing in the past, we have virtualized it now, so we must use past tense.