It looks like "PK" is being used in China as a slang word derived from the shorthand "Player Kill" not "Penalty Kick"... courtesy of western computer game imports.
The background is that in some of these role playing games, one can challenge some internet opponent to a duel: "Come on pk me!".
Now check out the Mandarin entry in this Wiktionary .
notletrest, I think this assessment is much much better than the penalty kick idea.
The jump from PK (player kill) to versus is an easy one:
In those computer games people meet to challenge one another to a duel and use the short hand PK as in the example
"Come on, PK me..."
And the logical jump I think is like this colloquial use of the word "versus"
"Come on, verse me!"
This is probably one of those non-standard use of the word becoming standard for good or worse. I first heard my kids say it (Australian Primary school age) a couple of years ago.
I did a little digging so you don't have to take my word, check this out. It looks like they are doing it in America as well.