his can be done in ANY game as long as it's in Ranked mode.
I got it legitimately on UKM3 by using Sektor and jumping in quickly with a lengthy kombo and then surprising them with a teleport uppercut. Sub-Zero's freeze is also useful across all games.
This is boostable as you can decline anyone easily, therefore choosing your challenger. If you are having trouble boosting and can't win it, try PMing the user you're against on the character select screen and asking them if they'll let you win a round with a flawless.
You only need to win one ROUND, not a match.